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EDUC. 

PSYCH. 

LIBRARY 


T 


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A   SYSTEM   OF  PHILOSOPHY. 


THE  PRINCIPLES 


PSYCHOLOGY. 


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PART    T. 

THE  DATA  OF  PSYCHOLOGY. 


HERBERT     SPENCER 


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PART  I. 


THE  DATA   OF   PSYCHOLOGY. 


fTjHiv?.s,3nr] 


3S^^^ 


CHAPTER   I. 


THE    NERVOUS    SYSTEM. 


§  1.  Tlie  lowest  animal  and  tlie  higliest  animal  present  no 
contrast  more  striking  than  that  between  the  small  self-mo- 
bility of  the  one  and  the  great  self-mobility  of  the  other.  A 
monad  passing,  apparently  with  some  rapidity,  across  the 
field  of  the  microscope,  really  advances  with  extreme  slow- 
ness :  its  velocity,  unexaggerated  by  combined  lenses, 
being  about  that  of  the  minute-hand  of  a  watch.  The  parts 
of  a  disturbed  sea-anemone  draw  themselves  together  with 
a  speed  which,  though  immensely  greater  than  that  of  a 
monad  through  the  water,  is  insignificant  as  measured  by  the 
speed  of  most  terrestrial  and  aerial  creatures.  Comparing 
the  movements  of  Protozoa,  or  of  Zoopliytes,  with  those  of 
Birds  that  keep  pace  with  railway  trains  or  those  Mammals 
that  gallop  a  mile  in  a  minute,  their  locomotive  powers  seem 
scarcely  appreciable.  Masses  being  supposed  equal,  the 
quantity  of  motion  generated  in  the  last  case  approaches  a 
million  times  that  generated  in  the  first. 

Contrasts  of  this  kind  exist  within  each  great  division  of 
the  animal  kingdom,  as  well  as  in  the  animal  kingdom 
taken  as  a  whole.  The  sub-kingdom  Annulosa  shows  us  an 
immense  difference  between  the  slow  crawling  of  worms 
and  quick  flight  of  insects.  Among  Mollusks  the  sluggish- 
ness of  the  Tunicata  is  no  less  marked  than  the  activity  of 
the    Ce^halojpoda.     And  between    the   inferior   or  water- 


4  ..!.?.I^— --TfiE   DATA   OP   PSYCHOLOGY. 

breatting  Vertchrata  and  superior  or  air-breatliing  Verte' 
hrata,  there  is  an  equally  conspicuous  unlikeness  in  energy 
of  movement. 

This  self-mobility  which  by  its  greater  amount  generally 
distinguishes  higher  animals  from  lower^  and,  indeed,  enters 
largely  into  our  conceptions  of  higher  and  lower,  is  displayed 
in  several  ways.  We  see  it  in  the  changes  of  attitude  that 
are  made  without  moving  the  body  from  place  to  place. 
We  see  it  in  the  transference  of  the  body  as  a  whole 
through  space  :  considering  this  transference  apart  from 
external  resistances  overcome.  And  we  see  it  in  the  over- 
coming of  resistances — ^both  those  of  media  and  those 
due  to  gravity.  All  these,  however,  are  manifestations  of 
one  ability — the  ability  to  generate  a  force  which  either 
shows  itself  as  momentum  or  would  generate  momentum 
but  for  a  counterbalancing  force.  And  it  is  in  this  general 
form  that  we  are  here  concerned  with  this  ability.  We  have 
to  contemplate  the  inferior  animals  as  being  generators  of 
very  small  quantities  of  actual  or  potential  motion,  and  the 
higher  animals  as  being  generators  of  relatively-immense 
quantities  of  actual  or  potential  motion. 

§  2.  With  what  internal  differences  are  these  differences 
of  external  manifestation  connected  ?  No  doubt  with 
several.  An  active  organism  contains  various  appliances 
no  one  of  which  can  be  spared  without  greatly  diminishing, 
or  quite  destroying,  its  activity. 

If  the  alimentary  system  be  incapacitated,  there  must  pre- 
sently result  a  decreased  power  of  generating  motion,  from 
lack  of  the  materials  whence  motion  is  obtained ;  and  hence 
the  fact,  conspicuous  throughout  the  animal  kingdom,  that 
along  with  much  locomotive  activity  there  goes  a  developed 
apparatus  for  taking  up  nutriment.  It  is  manifest,  too, 
that  there  cannot  be  great  self-mobility  unless  the  absorbed 
materials  are  efficiently  distributed  to  the  organs  which 
transform  insensible  motion  into  sensible  motion ;  and  thus 


THE   NERVOUS    SY& 


it  happens  tliat  as  we  ascend  from  creatures  wHcli  move 
little  to  creatures  wliicli  move  mucli,  we  meet  with  a  more 
and  more  evolved  vascular  system.  Similarly  with  the 
organs  for  separating  from  the  blood  the  substances  that 
have  yielded  up  their  contained  motion.  If  the  blood  be- 
comes choked  with  inert  matter^  there  necessarily  results  a 
decreased  genesis  of  motion ;  and  therefore,  as  we  see  on 
comparing  inactive  with  active  animals,  the  exaltation  of 
activity  is  accompanied  by  the  development  of  depurating 
structures.  Still  clearer  is  it  that  the  production  of  much 
motion,  and  the  resistance  to  those  forces  which  antagonize 
motion,  imply  parts  capable  of  bearing  great  strains — 
masses  of  dense  tissue  such  as  in  vertebrate  animals  form 
bones,  and  in  invertebrate  animals  form  dermal  frame- 
works ;  and,  accordingly,  as  we  ascend  from  creatures  that 
are  inert  to  creatures  that  are  vivacious,  we  advance  from 
weak  to  strong  skeletons,  internal  or  external.  Above  all 
it  is  self-evident  that  along  with  locomotive  activity  there 
must  exist  those  contractile  organs  which  are  the  imme- 
diate movers  of  the  limbs  and  consequently  of  the  body ; 
and  hence  the  direct  connection  between  absence  of  mus- 
cular fibres  and  extremely-small  self-mobility,  and  the  dii-ect 
connection  between  development  of  the  muscles  and  much 
self-mobility — connections  so  direct  as  to  make  it  at  first 
sight  seem  that  the  genesis  of  motion  varies  as  the  mus- 
cular development. 

-Remotely  dependent,  however,  as  the  genesis  of  motion 
is  on  digestive,  vascular,  respiratory,  and  other  structures ; 
and  immediately  dependent  as  it  is  on  contractile  struc- 
tures; its  most  important  dependence  remains  to  be  named. 
For  all  of  these  appliances  taken  together  can  do  nothing 
of  themselves.  The  muscles  are  but  instruments,  which 
remain  passive  until  their  power  is  evoked  by  the  structure 
which  uses  them ;  and  the  quantity  of  motion  they  then 
give  out  varies  according  to  the  demand  made  by  this 
exciting  and  controlling   structure.       In  other  words,  the 


6  THE    DA.TA   OF    PSYCHOLOGY. 

initiator  or  primary  generator  of  motion  is  tlie  Nervons 
System.  '^Vllcro  there  is  extremely  little  power  of  generat- 
ing motion^  as  among  tlic  Protozoa  and  the  inferior  Coelen- 
terata,  there  is  no  nervous  system.  Where  activity  begins 
to  show  itself  a  nervous  sj'stem  begins  to  be  visible.  And 
where  the  power  of  self-movement  is  great^  the  nervous 
system  is  comparatively  well  developed.  Though  the  mus- 
cular system  also  becomes  larger  and  better  organized ;  yet 
the  quantity  of  motion  produced  is  fundamentally  related  to 
the  degree  of  nervous  development.  Not^  indeed,  that  it  is 
so  related  with  anything  like  uniformity :  this  we  shall 
presently  see  that  it  cannot  be.  But  it  is  so  related  more 
uniformly  than  in  any  other  way.  A  few  typical  contrasts 
will  show  this. 

§  3.  The  absence  of  measurements  renders  detailed  com- 
parison among  the  various  classes  of  Mollusca  unsatisfactory. 
On  putting  side  by  side  the  extreme  terms,  however,  we 
find  an  unquestionable  difference  in  the  proportion  between 
the  nervous  system  and  the  rest  of  the  body.  The  sedentary 
Ascidians,  which  do  little  in  the  way  of  mo\dng  beyond 
occasionally  contracting  themselves,  severally  possess  only 
a  single  small  ganglion  with  its  fibres ;  but  Cephalopods  of 
the  dibranchiate  order,  which  are  active  creatures  that  dart 
tln-ough  the  water  fast  enough  to  catch  fish,  contain  masses 
of  nerve-tissue  that  bear  much  larger  ratios  to  their  total 
masses. 

It  is  with  annulose  animals  as  with  molluscous  animals — 
we  have  no  definite  estimates  of  the  sizes  of  their  nervous 
systems ;  and  hence  can  bring  in  evidence  only  the  marked 
diflerences.  As  before,  the  extreme  forms  supply  these. 
The  sluggish  annuloid  types,  when  contrasted  with  the 
energetic  kinds  of  Anmilosa,  present  decided  deficiencies  of 
nerve-substance ;  and  even  between  such  less-remote  orders 
as  the  tubicolous  Annelids,  leading  stationary  lives,  and  the 
decapodous    Crustaceans,  leading   active   lives,  a  kindred 


THE  NERVOUS   SYSTEM.  / 

difference  may  be  safely  asserted.  There  are  also^  in  some 
annulose  types  contrasts  between  tlie  nervous  system  in  the 
inactive  and  active  stages  of  the  same  individual.  The  feebly- 
moving  caterpillar  has  but  a  small  nervous  system;  the 
butterfly,  with  its  power  of  vigorous  flight,  has  a  relatively 
large  one;  and  during  the  intermediate  pupa-state,  in 
which  the  organization  is  being  adapted  to  this  more  viva- 
cious life,  a  rapid  growth  of  the  nervous  system  may  be  traced. 
It  is  in  the  Vertchrata,  however,  that  the  most  striking 
evidence  meets  us.  According  to  Leuret,  the  average  ratio 
of  the  brain  to  the  body  is — in  fishes,  1  to  5,668  ;  in  rep- 
tiles, 1  to  1,321  ;  in  birds,  1  to  212 ;  and  in  mammals,  1  to 
186.  Now  though  these  can  be  but  rude  approximations, 
since  there  are  great  differences  within  each  class,  and  since 
the  ratio  of  the  brain  to  the  body  is  not  the  ratio  of  the 
whole  nervous  system  to  the  body ;  yet  the  relations  they 
indicate  are  substantially  true.  Were  the  weight  of  the 
spinal  cord  and  the  nerves  added  to  that  of  the  brain  in 
each  case,  the  strengths  of  the  contrasts  would  be  consider- 
ably diminished ;  but  the  contrasts  would  still  be  strong. 
And  with  them  there  go  the  strong  contrasts  between  the 
activities  in  the  respective  classes — the  Fishes  that  swim  in 
a  medium  of  their  own  specific  gravity ;  the  Reptiles  of 
which  the  higher  have  to  support  the  weights  of  their 
bodies  as  they  move  about  over  the  land,  but  cannot  do 
this  for  long  together ;  the  Birds  and  Mammals  that  are  in 
constant  locomotion,  often  at  high  velocities.  Here, 

too,  the  alleged  connection  is  rendered  the  clearer  by  the 
approximate  uniformity  of  the  relative  amount  of  muscle. 
The  weight  of  muscle  in  a  fish  forms  something  like  as 
large  a  part  of  the  total  weight  as  it  does  in  a  reptile — 
perhaps  a  larger  part ;  and  a  reptile  is  scarcely  if  at  all 
inferior  to  a  bird  or  a  mammal  in  the  proportion  of  contrac- 
tile tissue  it  possesses.  Hence  it  becomes  manifest  that 
indispensable  as  is  contractile  tissue  to  the  genesis  of 
motion,  its    quantity  does   not   determine  the   quantity  of 


8  .  .  -  ■  ;^  J?^E   DATA   OP   PSYCHOLOGY. 

motion  generated.  Whereas^  notwitlistanding  tlie  many 
complicating  circumstances^  a  general  relation  between 
quantity  of  nerve  and  quantity  of  motion  is  traceable. 

There  are  special  cases  which  illustrate  this  relation.  I 
may  name  one — the  case  of  the  Porpoise.  A  Porpoise's 
brain  exceeds  greatly  in  size  the  brains  of  other  Mammals 
that  have  bodies  commensurate  with  its  own,  except 
that  of  Man  and,  perhaps,  that  of  the  Gorilla.  Such  a 
structure  in  a  creature  leading  so  simple  a  life,  is  a  serious 
difficulty  in  the  way  of  current  interpretations  ;  but  is  quite 
in  harmony  with  the  interpretation  here  given.  Porpoises 
accompanying  a  steam-vessel,  gambolling  and  making  ex- 
cursions on  either  side  without  apparent  effort,  prove,  by 
keeping  up  so  high  a  velocity  through  so  dense  a  medium, 
that  their  motor  energies  are  enormous. 

§  4.  A  closer  examination  of  the  facts  soon  reveals  the 
insufficiency  of  the  foregoing  generalization.  Deep  as  is 
the  connection  between  nervous  development  and  locomotive 
activity,  further  comparisons  show  that  it  is  complicated 
with  some  other  connection  scarcely  less  radical.  If,  other 
things  being  equal,  the  quantity  of  motion  generated 
varied  directly  as  the  quantity  of  nerve-tissue,  then,  in 
creatures  constitutionally  alike  or  but  little  dissimilar,  a 
tolerably  constant  ratio  would  exist  between  the  mass  of 
the  nervous  system  and  the  mass  of  the  body :  supposing 
the  body,  whether  large  or  small,  to  be  carried  from  place 
to  place  with  equal  velocity.  The  ratio  is  far  from  constant 
however. 

A  horse  gallops  much  faster  than  a  man  runs ;  and  a 
horse  in  ordinary  work  daily  moves  his  body  through  a 
space  greater  than  that  through  which  a  man  moves  his  body, 
or  greater  than  that  transposition  of  his  body  which  a  man's 
daily  labour  is  equivalent  to.  Hence  were  there  a  simple 
relation  between  amount  of  nerve-tissue  and  amount  of  mo- 
tion evolved,  a  horse,  which  weighs  some  seven  times  as  much 


THE   NERVOUS    SYSTEM 


^-POLIS:^ 


as  a  man^  should  have  a  nervous  system  at  least  seven  times 
as  heavy.  Instead  of  this  it  has  a  lighter  nervous  system.  Its 
brain  weighs  but  one  pound  seven  ounces;  and  were  its  spinal 
cord  added,  the  total  weight  would  probably  not  exceed  two 
pounds.  But  a  man's  brain  and  spinal  cord  weigh  between 
three  and  four  pounds.  Thus  the  horse's  cerebro-spinal 
axis  is  but  one-tenth  of  what  it  should  be,  were  this  relation 
the  only  one.  Still  clearer  is  the  proof  that  there 

is  some  other  relation,  when  we  avoid  modifying  causes,  by 
comparing  animals  of  the  same  genus,  or  species,  but  of 
different  sizes.  The  varieties  of  dogs  supply  good  illustra- 
tions. A  newfoundland  and  a  spaniel  are  alike  in  organiza- 
tion, food,  temperature,  respiration,  &c.  j  and  they  are 
approximately  alike  in  their  powers  of  locomotion :  the 
advantage  being  on  the  side  of  the  larger  of  the  two. 
Were  genesis  of  motion  measured  by  quantity  of  nerve- 
tissue,  a  newfoundland' s  cerebro-spinal  axis  should,  there- 
fore, exceed  in  size  that  of  a  spaniel  as  much  as  a  newfound- 
land's  body  exceeds  in  size  that  of  a  spaniel.  But  it  by  no 
means  does  so.  While  considerably  larger  absolutely,  it  is 
much  smaller  relatively. 

Consequently,  we  must  say  that  though  the  nervous 
system  is  the  initiator  of  motion,  and  though  there  is 
evidently  some  relation  between  degree  of  nervous  develop- 
ment and  degree  of  motor  energy;  yet  this  relation  is 
involved  with,  and  obscured  by,  another.  Let  us  re-examine 
the  facts  in  search  of  it. 

§  5.  In  what  other  way  than  in  relative  feebleness,  do  the 
motions  of  inferior  creatures  differ  from  those  of  superior 
creatures  ?  They  differ  in  relative  simplicity.  Animals 
that  are  but  little  evolved  perform  actions  which,  besides 
being  slow,  are  few  in  kind  and  severally  uniform  in  com- 
position. Animals  that  are  much  evolved  perform  actions 
which,  besides  being  rapid,  are  numerous  in  kind  and  seve- 
rally involved  in  composition.     The  movements  in  the  one 


10  THE    DATA   OF   PSYCHOLOGY. 

caso  are  small  and  liomogeiieous,  and  in  the  other  case 
great  and  heterogeneous.  Each  sub-kingdom  of  animals 
exemjilifies  this  second  general  relation,  as  much  as  it  does 
the  first. 

Humble  Mollusks,  like  the  fixed  Tunicata,  display  scarcely 
any  energies  beyond  those  required  to  contract  their  bodies 
when  distui'bed  and  afterwards  to  unfold  them.  But  in  the 
highly-organized  Cuttle-fishes,  besides  the  rapid,  quickly- 
varied,  and  well-adjusted  movements  exhibited  in  the  pur- 
suit and  capture  of  prey,  we  have  the  numerous  and  com- 
bined movements  of  the  suckered  arms,  used  not  only  for 
j^rehension  but  occasionally  for  travelling  over  solid  surfaces. 

The  Annulosa,  including  with  them  the  Annuloida,  supply 
a  like  general  contrast.  Between  the  uniform,  little-varied 
motions  of  a  Nemertine  worm,  and  the  multiform,  variously- 
combined  motions  of  the  Crab  or  the  Spider,  the  diSerence 
is  paralleled  by  the  difference  in  nervous  evolution.  And  a 
like  structural  contrast  accompanies  the  contrast  between 
the  few  simple  actions  of  the  caterpillar  and  the  numerous 
complex  actions  of  the  butterfly. 

But  that  heterogeneity  of  movement  increases  along  with 
relative  size  of  the  nervous  system,  is  best  shown  by  com- 
parisons among  vertebrate  animals.  Progressing  by  alter- 
nate contractions  of  its  lateral  muscles,  and  opening  its 
jaws  to  take  in  food  and  water,  the  Fish  adds  to  these  little 
else  but  those  undulations  of  the  fins  and  tail  that  serve  to 
balance  and  turn  it.  A  Ecptile,  using  its  limbs  in  the  water 
or  on  land  or  both,  performs  muscular  actions  considerably 
more  varied  and  more  combined ;  but  still,  actions  that  are 
directed  to  comparatively  few  ends.  An  ordinary  Mammal 
exhibits  in  the  chase  and  destruction  of  prey,  in  the  making 
of  burrows,  in  the  rearing  of  young,  in  the  laying  up  of 
food,  a  greater  variety  of  actions  that  are  severally  more 
compound.  On  arriving  at  the  higher  Mammals,  ending  with 
Man,  we  meet  Avith  motions  that  are  almost  countless  in 
their   kinds,   that  are   severally  composed  of  many  minor 


THE   NERVOUS    SYSTEM.  11 

motions  accurately  adjusted  iu  their  relative  quantities  and 
successions^  and  tliat  are  themselves  compounded  into 
courses  of  action  directed  to  multiform  objects.  And  witii 
eacli  sucli  increment  of  complexity  in  tlio  motor  functions 
tlirougliout  tlie  Vertchrata,  there  goes  an  increment  of 
nervous  endowment. 

Thisj  tlien^  is  the  secondary  connection  which  traverses 
and  complicates  the  primary  connection.  We  saw  that  were 
there  no  other  relation  than  that  between  quantity  of 
nerve-tissue  and  quantity  of  motion  generated,  a  Horse 
should  have  a  far  larger  nervous  system  than  a  Man, 
instead  of  having  a  smaller  one.  But  finding  that  there 
is  also  a  relation  between  quantity  of  nerve-tissue  and 
complexity  of  motion,  we  are  led  to  expect  an  excep- 
tionally large  nervous  system  in  Man;  and  are  enabled  to 
understand  why  he  has  a  larger  one  than  a  Horse  has.  More 
obvious,  because  not  involved  with  irrelevant  differences,  is 
the  interpretation  thus  yielded  of  the  general  rule,  already 
illustrated  in  the  case  of  the  Dogs,  that  in  each  natural 
group  or  order  of  Mammals,  the  nervous  systems  do  not  in- 
crease in  the  same  ratio  as  the  bodies.  We  will  glance  at 
another  illustration  of  this,  supplied  by  the  Priniafes;  specially 
instructive  because  of  the  significant  exception  it  contains, 
and  specially  interesting  because  that  exception  is  furnished 
by  mankind. 

The  small  monkeys  have  relatively  very  large  brains — 
larger  relatively  than  the  brains  of  their  congeners,  in- 
cluding even  the  highest.  This  connection,  parallel  to  that 
presented  in  the  spaniel  and  the  newfoundland,  has  a  parallel 
explanation.  The  movements  of  the  little  Capuchin  monkey 
are  approximately  as  varied  and  complex  as  those  of  the 
great  Gorilla ;  and  hence,  in  so  far  as  nervous  evolution  is 
related  to  heterogeneity  of  motion,  the  Capuchin  should  have 
a  nei'vous  system  differing  but  little  in  size  from  that  of  the 
Gorilla.  But  since  there  is  also  a  relation  between  quantity 
of  nerve  and  quantity  of  motion  generated,  the   Gorilla's 


12  THE    DATA   OP   PSYCHOLOGY. 

nervous  system  must  be  absolutely  greater  tbougb  relatively 
smaller :  which  we  fiud  it  to  be.  Between  the  Gorilla  and 
Man,  however,  there  exists  a  converse  contrast.  Heavier 
than  a  Man,  and  moving  about  in  the  trees,  a  Gorilla  pro- 
bably generates  daily  as  much  motion  as  a  savage,  or  as  a 
civilized  labourer ;  and  were  it  the  sole  function  of  nerve- 
tissue  to  originate  motion,  should  have  at  least  as  large  a 
nervous  system.  But  the  nervous  system  of  Man  is  twice 
as  heavy.  Here,  therefore,  all  other  relations  being  sub- 
stantially the  same,  and  the  physiological  processes  being 
approximately  alike  in  the  two  cases,  the  relative  largeness 
of  the  human  nervous  system  stands  clearly  related  to  the 
relatively-enormous  complexity  of  human  actions — a  com- 
plexity shown  partly  in  the  more  compound  simultaneous 
movements,  but  mainly  in  the  combination  of  successive 
movements,  simple  and  compound,  directed  to  remote 
ends. 

§  6.  This  double  relation  must  still  be  taken  as  ap- 
proximate only.  Seeing  as  we  did  at  the  outset  that  the 
genesis  of  motion  depends  on  many  physiological  conditions, 
of  which  each  is  separately  variable,  it  is  manifest  that 
the  fundamental  connections  we  have  traced  must  have 
sundry  minor  irregularities.  AVithout  treating  of  these  in 
detail,  it  may  be  well  to  instance  one — that  due  to  differ- 
ence of  bodily  temperature.  Birds  as  a  class  are  more 
active  than  Mammals  as  a  class;  and  though  many  Mammals 
go  through  motions  more  heterogeneous  than  those  of  Birds, 
yet  the  inferior  Mammals  can  scarcely  be  said  to  exceed 
Birds  in  the  heterogeneity  of  their  motions.  Nevertheless, 
the  nervous  systems  of  Birds  are  relatively  somewhat 
smaller  than  the  nervous  systems  of  Mammals.  The  explana- 
tion is  that  Birds  have  a  higher  blood-heat  with  its  accom- 
panying more  active  respiration — both  implying  a  greater 
rate  of  molecular  change.  And  a  greater  rate  of  molecular 
change  enables  a  smaller  nervous  system  to  generate  an 


THE   NEEVOUS    SYSTEM.  13 

amount  of  motion  wliicli  would  require  a  larger  nervous 
system  if  the  rate  of  molecular  change  were  less. 

A  further  qualifying  fact  to  be  here  named  is  that,  all 
other  things  being  equal,  the  power  of  a  nervous  system 
does  not  vary  exactly  as  its  mass.  For  reasons  that  will 
hereafter  appear,  its  efficiency  as  a  motor  agent  increases 
in  a  somewhat  higher  ratio  than  the  quantity  of  matter  it 
contains. 

But  after  all  modifying  causes  have  been  allowed  for, 
there  remain  substantially  intact  the  fundamental  rela- 
tions set  forth — namely,  that  wherever  much  motion  is 
evolved,  a  relatively-large  nervous  system  exists;  that 
wherever  the  motion  evolved  though  not  great  in  quantity 
is  heterogeneous  in  kind,  a  relatively -large  nervous  system 
exists;  and  that  wherever  the  evolved  motion  is  both  great 
in  quantity  and  heterogeneous  in  kind,  the  largest  nervous 
systems  exist. 

§  7.  It  is  with  deliberate  intention  that  I  have  set  out 
with  this  unfamiliar  and,  as  many  will  think,  somewhat 
strange  presentation  of  the  facts.  My  reasons  for  doing  so 
are  several. 

One  of  them  is  that  we  are  here  primarily  concerned  with 
psychological  phenomena  as  phenomena  of  Evolution ;  and, 
under  their  objective  aspect,  these,  reduced  to  their  lowest 
terms,  are  incidents  in  the  continuous  re-distribution  of 
Matter  and  Motion.  Hence  the  first  question  respecting 
the  nervous  system  as  studied  from  our  point  of  view  is — 
what  are  the  leading  facts  it  presents  as  expressed  in  terms 
of  Matter  and  Motion  ? 

Another  reason  is  that,  apart  from  any  doctrine  of  Evolu- 
tion, true  conclusions  respecting  psychical  phenomena  must 
be  based  on  the  facts  exhibited  throughout  organic  nature ; 
and  that  the  above  statement  does  literally  nothing  else 
than  express  these  facts — expresses,  too,  all  that  direct 
induction  can  tell  us  respecting  their  essential  relations. 


14  THE    DATA   OP   PSYCHOLOGY. 

The  actions  of  all  organic  beings,  including  those  of  our 
own  species,  arc  known  to  us  only  as  motions.  Shutting 
out  our  inferential  interpretations,  the  leaps  and  doublings 
of  the  escaping  prey  in  common  with  the  variously-adapted 
and  rapidly-changed  actions  of  the  pursuer,  are,  to  our  per- 
ceptions, nothing  but  movements  combined  in  particular 
ways ;  and  so  too  are  the  changes  of  expression,  tones  of 
voice,  and  verbal  articulations  of  our  fellow-beings,  on  which 
we  put  such  hidden  implications.  As,  then,  science  requii'es 
us  to  distinguish  the  facts  as  actually  presented  from  the 
suppositions  we  ordinarily  join  with  them,  it  is  needful  to 
exhibit,  in  all  its  nakedness,  this  primordial  relation  between 
the  external  motions  and  their  internal  originator. 

Yet  a  further  reason  for  setting  out  thus,  is  that  we  so 
escape  from  pre-conceptions.  Those  who  bring  with  them 
to  the  investigation  of  psychical  phenomena,  the  hypotheses 
that  have  descended  to  us  from  the  past,  are  almost  sure  to 
be  more  or  less  biassed  thereby.  While  intending  to  avoid 
assumptions  they  are  in  great  danger  of  having  their  con- 
clusions vitiated,  if  not  by  some  ancient  or  medireval  idea 
under  its  overt  form,  yet  by  corollaries  from  it  that  have 
unobtrusively  embodied  themselves  in  unsuspected  pos- 
tulates. As  we  shall  presently  see,  even  physiologists  have 
been  in  some  cases  thus  misled. 

Hence,  then,  without  at  all  calling  in  question  the  truth 
of  those  other  and  quite  different  interpretations  of  nervous 
phenomena  that  are  tacitly  expressed,  in  ordinary  language, 
it  is  proper  for  us  here  to  ignore  them.  Before  studying 
the  facts  from  a  psychological  point  of  view,  we  have  first  to 
study  them  from  a  physiological  point  of  view.  The  pri- 
mary truth  disclosed  by  the  facts  as  so  studied,  is  the 
universality  of  this  relation  between  the  degree  of  nervous 
evolution  and  the  quantity  and  heterogeneity  of  the  pro- 
duced motion.  We  now  pass  to  the  secondary  truths 
similarly  disclosed. 


CHAPTER  II. 

THE    STRUCTURE    OF    THE    NERVOUS    STSTElf. 

§  8.  An  outline  of  nervous  structure  must  precede  a 
detailed  account  of  it ;  and  tlie  essential  facts  to  be  indi- 
cated in  an  outline  may  be  brouglit  most  clearly  into  view  by 
comparing  with,  one  anotlier  the  nervous  systems  possessed 
by  different  types,  and  by  different  grades  of  the  same  type. 
We  will  limit  our  comparisons  to  the  thi-ee  superior  sub- 
kingdoms  of  animals. 

A  minute  nodule  with  diverging  threads  constitutes  the 
rudimentary  nervous  system,  as  existing  in  the  lowest 
Mollusk.  In  the  Lamellibranchs  several  such  minute 
nodules,  or  ganglia,  are  distributed,  usually  in  pairs,  in 
different  parts  of  the  body;  and  beyond  th§  free  fibres 
which  they  severally  give  off  to  neighbouring  organs,  there 
are  fibres  by  which  they  are  connected  together.  Gastero- 
pods,  considerably  higher  in  organization  and  activity,  have 
nervous  centres  among  which  a  considerable  heterogeneity 
is  produced  by  the  greater  size  of  some  than  of  others.  And 
besides  a  local  integration  of  paired  ganglia  iuto  single  bi- 
lobed  ganglia,  there  is  an  advance  in  general  integration^ 
shown  by  a  clustering  of  the  more  important  ganglia  about 
the  head.  The  Cephalopods,  and  especially  the  dibranchiate 
division  of  them,  in  which  the  molluscous  type  reaches  its 
highest,  show  us,  carried  still  further,  that  integration  of 
the  nervous  system  due  to  simple  growth,  joined  with  that 


16  THE    DATA    OF    PSYCHOLOGY. 

iutegration  due  to  concentration  and  coalescence  of  indepen- 
dent centres  ;  and  tliey  also  show  us  tlie  differentiations 
involved  by  tlieir  changes  of  size^  form,  and  distribution. 

A  delicate  cord  running  from  end  to  end  of  the  body,  and 
giving  off  lateral  fibres  in  pairs,  constitutes  the  nervous 
system  in  the  loAver  Annulosa.  When  from  limbless 
Annelids  we  pass  to  the  Articulate  types,  composed  of  seg- 
ments bearing  limbs,  we  find  the  nervous  system  formed  of 
a  series  of  centres,  each  sending  fibres  to  the  different  organs 
of  its  own  segment,  and  all  of  them  united  by  a  thick 
cord  of  fibres  with  a  fused  cluster  of  similar  centres 
in  the  head.  In  the  higher  Articulata  there  is  an  increased 
relative  size  of  the  nervous  centres  as  compared  with  their 
connecting  structures ;  an  actual  approach  of  the  chief 
nervous  centres  to  one  another,  both  longitudinally  and 
laterally ;  and  a  final  coalescence  of  them.  This  integration 
disclosed  by  comparisons  of  lower  and  higher  types,  may 
also  be  observed  in  progress  during  the  development  of  the 
individual  insect  or  the  individual  crustacean.  Ajtid  along 
with  advancing  growth,  consolidation,  and  combination  of 
nervous  structures,  there  may  be  traced  an  increasing  un- 
likeness,  both  among  the  central  masses  themselves, 
among  their  connecting  cords,  and  among  their  divergent 
fibres. 

Such  traits  of  evolution  are  exhibited  under  another  form 
in  the  vertebrate  sub-kingdom.  Its  lowest  known  member^ 
the  AmpJiioxus,  has  a  simple  cranio-spinal  axis,  the  anterior 
extremity  of  which  is  not  made  appreciably  different  from 
the  rest  by  development  of  distinct  cerebral  ganglia,  and 
which  gives  off  lateral  nerves  that  have  but  minor  dis- 
similarities. The  cj^clostome  Fishes,  possessed  of  cerebral 
ganglia  that  are  tolerably  manifest,  lead  us  to  the 
ordinary  fishes,  in  Avhicli  these  ganglia,  individually  much 
larger,  form  a  cluster  of  masses,  or  rudimentary  brain. 
Here,  however,  though  in  contact,  they  preserve  a 
serial  arrangement :  their  aggregation  is  little  more  than 


THE    STRUCTURE    OP   THE    NERVOUS    SYSTEM.  ]  7 

that  of  close  linear  succession.  But  in  tlie  liigliest  fishes 
certain  of  them  which  have  greatly  increased,  overlap  the 
others ;  and  tend  so  to  form  a  more  compact,  as  well  as  a 
larger,  aggregate.  Superior  Reptiles  and  Birds  display  this 
relative  increase  of  certain  of  the  clustered  ganglia,  and  con- 
sequent obscuration  of  the  rest,  in  a  greater  degree.  It  is 
carried  still  further  in  the  inferior  Mammals.  From  them 
upwards,  the  leading  change  of  nervous  structure  is  an 
augmentation  of  the  two  largest  pairs  of  these  aggregated 
nervous  centres.  In  Man  one  pair  has  become  so  enormous 
that  the  others  are  most  of  them  hidden  by  it,  and  nearly 
merged   in  it.  Along  with  this   direct   inte- 

gration there  goes  on  the  indirect  integration  constituted 
by  more  intimate  and  multiplied  connections.  These 
are  both  longitudinal  and  transverse.  While  in  the 
Amphioxus,  the  cranio-spinal  axis  contains  but  a  small 
proportion  of  the  nerve-fibres  which,  running  longitudinally, 
serve  to  unite  its  diSerent  parts ;  in  a  superior  vertebrate 
animal,  such  uniting  nerve-fibres  are  among  the  chief  com- 
ponents of  the  cranio-spinal  axis.  And,  similarly,  while  the 
lateral  halves  of  the  cerebrum  are  but  slightly  connected  in 
Birds,  and  have  connections  that  are  relatively  deficient  in 
the  inferior  Mammals,  they  become,  in  the  highest  Mammals, 
joined  together  by  a  thick  mass  formed  of  innumerable 
fibres.  Meanwhile  there  have  been  arising  diffe- 

rentiations no  less  conspicuous.  Beyond  that  general  one 
due  to  development  of  the  anterior  end  of  the  cranio- 
spinal axis  into  cerebral  ganglia ;  and  the  further  one 
of  like  nature  which  results  from  the  relatively  -  enor- 
mous growth  of  some  of  these  ;  other  differentiations 
have  been  constituted  by  the  local  unlikenesses  of  structure 
simultaneously  established.  As  they  enlarge,  the  greater 
ganglia  are  rendered  externally  dissimilar  from  the  rest  by 
the  formation  of  folds  or  convolutions  ;  and  their  internal 
parts  severally  acquire  distinctive  characters.  The  same 
thing  holds  of  the  peripheral  nervous  system.  Pairs  of 
*2 


18^  THE   DATA   OF    PSYCHOLOGY. 

nerves  that  were  originally  almost  uniform^  are  rendered 
multiform  by  tlie  much  greater  growth  of  some  than  of 
others,  and  by  the  inner  differences  that  accompany  these 
outer  differences. 

This  cursory  survey  of  the  nervous  system  under  the 
various  forms  it  presents  throughout  the  animal  kingdom, 
suffices  to  show  how  its  evolution  conforms  to  the  laws  of 
evolution  in  general.  We  are  also  shown  by  it  what  here 
more  immediately  concerns  us — that  while  the  rudimentary 
nervous  system^  consisting  of  a  few  threads  and  minute 
centres,  is  very  much  scattered,  its  increase  of  relative  size 
and  increase  of  complexity,  go  hand  in  hand  with  increased 
concentration  and  increased  multiplicity  and  variety  of  con- 
nections. Carrying  with  us  this  general  conception,  let  us 
now  study  its  structure  more  closely  :  considering,  at  firet, 
not  any  particular  forms  of  it  but  its  universal  form. 

§  9.  The  nervous  system  is  composed  of  two  tissues,  which 
both  differ  considerably  from  those  composing  the  rest  of  the 
organism.  They  are  usually  distinguished  from  one  another 
by  their  colours  as  grey  and  white,  and  by  their  minute  struc- 
tures as  vesicular  aud  fibrous.  Chemical  analyses  have  not 
at  present  thrown  more  than  a  flickering  light  on  the  consti- 
tution of  nerve-matter  in  general,  or  on  the  constitution  of 
one  kind  of  nerve-matter  as  contrasted  with  the  other.  All 
that  can  be  asserted  with  safety  is,  that  each  kind  contains 
phosphatic  fats  and  protein-substances;  but  that  these  com- 
ponents are  both  differently  disti-ibuted  and  in  different 
states  in  the  two  tissues.  Let  us  see  what  we  are  told 
about  them  by  the  microscope,  aided  by  chemical  re-agents. 

AVhere  their  evolution  can  be  traced,  the  vesicles  or  cor- 
puscles of  the  grey  tissue  appear  to  take  their  rise  out  of  a 
nitrogenous  protoplasm,  full  of  gi-anules  and  containing 
nuclei.  Round  these  nuclei  the  protoplasm  aggregates  into 
spheroidal  masses,  which,  becoming  severally  inclosed  in 
delicate  membranes  (in  many  cases  inferred  rather  than  seen) 


THE  STRUCTURE  OF  THE  NERVOUS  SYSTEM.        19 

are  so  made  into  nerve-cells.  The  protein-substance,  tlius 
forming  alike  the  chief  contents  of  the  nerve-cells  and  the 
chief  part  of  their  matrix,  is,  though  coagulated,  soft.  The 
granules  imbedded  in  it,  both  within  and  without  the  cells, 
consist  of  fatty  matter.  And  on  comparing  together  nerve- 
cells  in  different  stages,  there  are  seen  differences  in  the 
colours  of  the  granules,  indicating  a  progressive  meta- 
morphosis. To  complete  a  general  idea  of  the  grey  tissue, 
it  must  be  added  that  the  more  developed  of  these  nucle- 
ated cells,  or  nerve-corpuscles,  give  off  processes,  usually 
branched,  that  vary  in  number  and  degree  of  ramification ; 
that  among  the  corpuscles  and  their  branches  are  dis- 
tributed the  terminations  of  nerve-fibi*es ;  and  that  while  in 
some  nervous  centres  it  is  common  for  these  fibres  to  run 
directly  into  the  cells  or  to  be  continuous  with  certain  of 
the  processes,  in  other  nervous  centres  the  connections 
between  fibres  and  cells  are  rarely  if  ever  direct,  but  where 
they  exist,  are  made  through  the  remote  sub-divisions  of 
branches  given  off  by  both. 

Wlien  we  pass  to  the  white  or  fibrous  tissue,  we  meet  with 
matters  that  at  first  sight  appear  as  distinct  from  the  others 
in  nature  as  in  mode  of  arrangement.  The  fibres  prove  to 
be  minute  tubes.  Within  the  extremely  delicate  membrane 
of  which  each  tube  is  formed,  there  is  a  medullary  substance 
or  pulp,  which  is  viscid  like  oil,  has  a  pearly  lastre,  and 
consists  of  albuminous  and  fatty  substances.  But  unlike  as 
the  contents  of  the  nerve-tubes  and  the  nerve-cells  thus 
appear  to  be,  a  careful  scrutiny  discloses  between  them  an 
essential  kinship.  For  imbedded  in  the  pulp  which  fills  the 
tube  or  sheath,  there  lies  a  delicate  fibre,  or  ''  axis-cylinder," 
which  is  composed  of  a  protein-substance.  Though 
chemically  similar  to  the  protein-substance  contained  in  the 
cells  of  the  vesicles,  this  is  physically  different ;  since,  besides 
being  comparatively  firm  or  solid,  it  is  uniform  and  con- 
tinuous, instead  of  having  its  continuity,  broken  by  fat 
granules.     That  this  central  thread  of  protein-substance  is 


20  THE    DATA   OP    PSYCHOLOGY. 

tliG  essential  nerve,  to  wliicli  tlie  slieath  of  medullary  matter 
witli  its  surrounding  membranous  slieath  are  but  acces- 
sorieSj  tlicre  are  several  proofs.  One  is  tliat  in  tlie  lower 
animalSj  as  well  as  in  tbc  embryos  of  the  higher,  no  me- 
dullary sheaths  exist :  the  nerve  consists  of  the  axis-cylinder 
and  its  protecting  membrane,  without  any  pulp  lying 
between  them.  Another  proof  is  that  at  the  peripheral  ter- 
minations of  nerves,  even  in  superior  animals,  the  medullary 
sheath  commonly,  if  not  always,  stops  short ;  while  the  cen- 
tral thread,  covered  by  the  outermost  membrane,  continues 
further,  and  ends  in  delicate  ramifications  not  inclosed  in 
distinguishable  sheaths.  And  a  further  proof  is  that  where 
a  nerve-fibre  unites  with  a  nerve-cell,  the  medullary  sheath 
ceases  before  arriving  at  the  place  of  union  ;  while  the  axis- 
cylinder  joins  the  contents  of  the  cell,  and  its  protecting 
membrane  becomes  continuous  with  the  cell-wall,  where  this 
exists.  Hence  concluding,  as  we  are  warranted  in  doing, 
that  the  axis-cylinder  is  its  essential  part,  we  see  that 
the  matter  of  nerve-fibre  has  much  in  common  with  the 
matter  of  nerve-vesicle  :  the  differences  between  them  ap- 
pearing to  be  mainly  that,  in  the  nerve-vesicle,  the  protein- 
substance  contains  more  water,  is  mingled  with  fat- 
granules,  and  forms  part  of  an  obviously  unstable  mass; 
whereas  in  the  nerve-tube  the  protein-substance  is  denser, 
and  is  distinctly  marked  off  from  the  fatty  compounds  that 
surround  it :  so  presenting  an  arrangement  that  is  relatively 
stable. 

Wliat  is  the  meaning  of  this  difference  ?  Before  seeking 
an  answer  we  must  remember  that  compound  substances 
undergo  two  fundamentally  different  kinds  of  metamorphosis 
— one  in  which  the  components  are  some  or  all  of  them  dis- 
sociated and  distributed  through  surrounding  space,  either 
apart  or  in  new  combinations ;  and  one  in  which  the  com- 
ponents, instead  of  being  dissociated,  are  merely  re-ar- 
ranged, so  as  to  alter  the  perceptible  properties  of  the 
mass  without  destroying  its  physical  continuity.     The  first 


THE  STRUCTUKE  0¥   THE  NERVOUS  SYSTEM.        21 

we  call  decomi30sition ;  tlic  second  isomeric  transforma- 
tion. These  forms  of  cliange  are  further  distinguished 
in  this,  that  the  one  is  usually  accompanied  by  a  great 
dissipation  of  motion,  whereas  the  motion  given  out 
or  taken  up  along  with  the  other  is  relatively  insignificant. 
There  is  yet  a  third  contrast.  After  decomposition  the 
separated  components  cannot  be  readily  made  to  resume 
their  previous  relations  :  often  it  is  impossible  to  combine 
them  again;  and  in  most  other  cases  it  is  diilicult  to  do  this. 
But  in  many  instances  of  isomeric  transformation,  resump- 
tion of  the  original  form  may  be  produced  by  a  very 
moderate  change  of  conditions. 

Now  the  two  kinds  of  molecular  change  thus  strongly 
contrasted,  are  the  two  kinds  of  molecular  change  which  we 
have  reason  to  suspect  are  undergone  by  the  two  forms  of 
nervous  matter.  While  the  protein-substance  mingled  with 
fat-granules  in  the  vesicles,  is  habitually  decomposed;  the 
protein-substance  forming  the  axes  of  the  nerve-fibres  is 
habitually  changed  from  one  of  its  isomeric  states  to  another. 
Such,  at  least,  is  the  assumption  here  made,  in  conformity 
with  the  conclusion  drawn  in  the  Frinciples  of  Biology 
(§  302) ;  where  it  was  argued  that  the  propagation  of  mole- 
cular disturbances  from  one  place  in  an  organism  to  another, 
tends  so  to  modify  the  mingled  colloidal  substances  as  to 
produce,  between  the  two  places,  a  form  of  colloid  that 
undergoes  isomeric  transformation  when  distm-bed,  and  com- 
municates the  disturbance  in  undergoing  the  transformation; 
and  where  it  was  argued  that  this  easily-transformable 
colloid,  having  had  such  a  change  set  up  at  one  end  of  it 
and  passed  on  to  the  other,  giving  out  in  the  process  some 
molecular  motion  and  consequently  falling  in  temperature, 
immediately  re-absorbs  from  the  adjacent  tissues  permeated 
by  blood,  an  amount  of  molecular  motion  equal  to  that  which 
was  lost :  thereupon  resuming  its  previous  isomeric  state,  and 
its  fitness  for  again  propagating  a  wave  of  transformation. 

Much  as  there  is  here  of  hypothesis,  the  indirect  evidence 


22  THE    DATA   OF   PSYCHOLOGY. 

makes  it  probable  that  if  tliis  is  not  tlio  true  interpretation^ 
tlic  true  interpretation  is  analogous  to  it.  That  the  matter 
contained  in  the  vesicles  is  the  seat  of  destructive  molecular 
chau'i^es,  Avith  accompanying  disengagement  of  motioUj 
while  the  matter  contained  in  the  tubes  is  the  seat  of 
changes  which,,  of  whatever  special  nature,  do  not  involve 
much  destructive  decomposition  and  disengagement  ol 
motion^,  are  beliefs  for  which  we  have  several  warrants ; — 
among  others,   the  following.  The  grey  tissue 

contains  far  more  water  than  the  white  tissue  :  the  propor- 
tion of  solids  to  water  being  about  12  per  cent,  in  the  grey 
tissue,  while  in  the  white  tissue  it  is  some  25  per  cent. 
Now  abundance  of  water  facilitates  molecular  change,  and^ 
habitually  characterizes  parts  in  which  the  rate  of  molecular 
change  is  high.  Hence  the  implication  is  that  the  grey 
matter  undergoes  metamorphosis  with  much  greater  rapidity 
than  the  white.  Stronger  evidence  is  afforded  by  the 

fact  that  the  grey  or  vesicular  substance  has  a  vascularity 
immensely  exceeding  that  of  the  white  or  fibrous  sub- 
stance. On  comparing  the  net-works  of  blood  vessels  that 
permeate  the  two,  the  difference  is  consi^icuous ;  and  it  is 
much  greater  than  at  first  appears.  An  estimate  based  on 
measurements,  proves  that  a  given  bulk  of  the  one  contains 
about  five  times  as  many  capillaries  as  an  equal  bulk  of  the 
other.*    Now  since  these  minute  canals  that  bring  and  take 

*  The  drawing  on  which  this  estimate  is  based,  is  contained  in  the  Manual 
of  Human  Histology,  by  A.  Kolliker  :  translated  and  edited  by  George  Busk, 
F. U.S.,  and  Thomas  Huxley,  F.R.S.  The  estimate  is  easily  made.  A 
number  of  equi-distant  parallel  lines  being  drawn  transversely  through  the  two 
net-works,  the  number  of  places  at  which  one  of  these  lines  crosses  blood-vessels 
within  a  given  length  (say  an  inch)  is  counted,  and  the  like  being  done  with 
an  equal  length  of  each  of  the  other  parallel  lines  traversing  the  same  net- 
work, there  is  obtained,  by  taking  an  average,  the  number  of  vessels  usually 
met  with  in  a  specified  distance.  The  like  process  is  then  gone  through  with 
lines  of  the  same  length  traversing  the  other  net-work.  These  averages  do 
not,  however,  truly  express  the  comparative  numbers  of  such  intersections  in 
the  two  net-works  ;  since  the  meshes  of  the  one  are  unlike  those  of  the  other 
in  shape.     Hence  it  is  needful  to  draw  an  equal  number  of  parallel  longitu- 


THE  STRUCTURE  OP  THE  NERVOUS  SYSTEM.        23 

TuWay  materials,  must  be  numerous  in  proportion  as  com- 
position and  decomposition  are  quick ;  we  may  infer  a  p^reat 
difference  between  the  rates  of  destructive  change  in  tlie 
two  tissues.  Another  contrast  supports  this  con- 

chision  no  less  strongly.  The  unstable  granular  protoplasm 
contained  in  the  corpviscles,  is  shielded  from  adjacent  dis- 
turbing forces  by  a  menibi\ane  which,  even  where  thickest, 
is  so  delicate  that  its  existence  can  be  demonstrated 
only  by  the  help  of  re-agents ;  and  which  in  many 
corpuscles  cannot  be  made  visible  at  all.  Hence  between 
the  matter  contained  in  these  corpuscles,  or  vesicles, 
and  the  streams  of  blood  that  run  among  them  so 
abundantly,  are  interposed  little  else  than  the  delicate  walls 
of  the  capillary  blood-vessels ;  and  thus  the  disturbing 
substances  brought  by  each  capillary,  can  pass  with  the 
least  possible  hindrance  into  the  unstably-arranged  contents 
of  the  neighbouring  vesicles.  Quite  otherwise  is  it  with 
the  relations  of  the  blood  to  the  contents  of  nerve-tubes. 
The  wall  of  each  nerve-tube  is  thick  enough  to  make  it 
easily  demonstrated ;  and  between  it  and  the  central  thread 
of  essential  matter,  comes  the  coat  of  nerve-medulla. 
Through  these  barriers  the  disturbing  agents,  carried  among 
the  nerve-tubes  by  sparingly-distributed  capillaries,  cannot 
readily  pass  ;  and  the  essential  nerve-thread  is  prevented  from 
having  molecular  changes  set  up  in  it  at  places  between 
its  two  extremes.  This  protection  suffices  so  long  as  the 
disturbino-  agjents  remain  normal  in  their  amounts  ;  but  when 
they  become  excessive,  as  they  do  if  the  blood-vessels  become 
congested,  local  changes  in  the  nerve-threads  are  caused  : 
whence  one  kind  of  neuralgia.     It  should  be  added  that  by 

dinal  lines  ;  and  to  repeat  with  them  this  process  of  averaging.  By  taking  tho 
means  between  the  resulting  numbers  and  the  previous  numbers,  we  get  a  cor- 
rect representation  of  the  relative  frequencies  with  which  the  vessels  occur  in 
space  of  one  dimension.  To  ascertain  their  relative  frequencies  in  space  of 
three  dimensions,  or  in  solid  tissue,  it  is  of  course  needful  simply  to  cube  the 
two  numbers  so  arrived  at. 


24  ■  THE    DATA   OF   PSYCHOLOGY. 

this  sheathing  of  nerve-medulla,  the  essential  nerve-threads, 
besides  being  shielded  against  disturbances  from  neighbour- 
ing currents  of  blood,  are  shielded  against  disturbances  from 
nerve-threads  in  the  same  bundle.  Were  "  axis-cylinders  " 
lying  in  lateral  contact  not  thus  coated,  a  molecular  change 
propagated  through  one  would  set  up  molecular  changes  in 
its  neighbours;  as,  in  fact,  it  does  in  an  early  stage  of 
ataxy,  characterized  by  loss  of  the  medullary  sheaths. 
Hence,  too,  the  explanation  of  that?  normal  absence  of  me- 
dullary sheaths  which  sundry  nervous  structures  show  us. 
For  amono'  the  Invcrtehrata,  in  which  this  normal  absence 
occurs,  the  fibres  contained  in  the  same  bundle  have 
nothing  like  those  many  and  varied  distinctions  which  they 
have  in  the  higher  animals :  they  have  termini  of  which 
the  structures  and  functions  are  much  less  differentiated. 
Similarly  with  those  bundles  of  grey  or  non-medullated 
fibres,  contained  in  the  sympathetic  system  of  vertebrate 
animals ;  for  these  bundles,  serving  to  establish  relations 
anions'  the  viscera,  each  of  which  is  much  less  divided  into 
parts  that  act  independently,  there  needs  no  such  perfect  in- 
sulation of  the  nerve-fibres.  And  the  like  holds  even  in  cer- 
tain portions  of  the  peripheral  cerebro-spiiial  system ;  as  the 
olfactory  expansion,  Avhich  consists  of  an  extensive  plexus 
of  non-medullated  fibres,  and  which  has  the  peculiarity 
that  difierent  parts  of  its  area  are  not  acted  upon  sepa- 
rately. 

The  evidences,  direct  and  indirect,  thus  justify  us  in 
concluding  that  the  nervous  system  consists  of  one  kind 
of  matter  under  difierent  forms  and  conditions.  In  the 
grey  tissue  this  matter  exists  in  masses  containing-  cor- 
puscles, which  are  soft  and  have  granules  dispersed  through 
them,  and  which,  besides  being  thus  unstably  composed, 
are  placed  so  as  to  bo  liable  to  disturbance  in  the  greatest 
possible  degree.  In  the  white  tissue  this  matter  is  collected 
together  in  extremely  slender  threads,  that  are  denser,  that 
arc  uniform  in  texture,  and  that  arc  shielded  in  an  unusual 


THE    STRUCTURE    OP   THE   NERVOUS    SYSTEil.  25 

manner  from  disturbing  forces,  except  at  tlieir  two  extre- 
mities. And  tlie  implication  on  wliicli  we  hencefortli  pro- 
ceed is,  that  the  masses,  unstably  constituted  and  con- 
ditioned, are  seats  of  destructive  molecular  changes,  and 
disengagement  of  motion ;  while  the  stably  constituted  and 
conditioned  threads,  are  the  seats  of  molecular  changes  that 
are  not  destructive,  and  are  probably  isomeric. 

§  10.  Nerve-tubes  with  their  contained  protein-threads, 
and  nerve-cells  with  their  contained  and  surrounding 
masses  of  changing  protein-substance,  are  the  histologic 
elements  of  which  the  nervous  system  is  built  up ; 
and  we  have  now  to  ask  in  what  way  they  are  put 
together.  We  will  begin  with  the  peripheral  termina- 
tions of  the  nerve-tubes  ;  or  rather,  with  those  of  them 
which  lie  on  the  outer  surface. 

Suppose  the  skin,  including  those  introverted  portions 
of  it  which  form  the  receptive  areas  of  the  special 
senses,  to  be  marked  all  over  in  such  a  way  as  to  form  a 
net-work.  Suppose  the  meshes  of  this  net-work  to  vary 
extremely  in  their  sizes ;  so  that  while  in  some  places  they 
are  as  large  as  those  of  a  fishing-net,  they  are  in  other  places 
not  large  enough  to  admit  the  point  of  a  needle.  Or,  to 
speak  specifically,  suppose  that  on  the  middle  of  the  back 
the  meshes  are  somi3  2h  inches  in  diameter,  and  that  being 
equally  large  over  the  middles  of  the  fore-arms,  and  the 
middles  of  the  thighs,  they  diminish  to  2  inches  and  less 
over  the  neck  and  breast,  to  1^  inches  at  the  extremities 
of  the  legs,  to  1  j  inches  on  the  backs  of  the  hands,  to  less 
than  an  inch  on  the  forehead,  to  less  than  half-an-inch  over 
the  cheeks  and  over  the  palms  of  the  hands,  to  a  quarter 
of  an  inch  and  less  over  the  fingers,  to  a  twelfth  of  an  inch 
at  the  inner  tips  of  the  fingers,  and  at  the  tip  of  the  tougue 
to  one  twenty-fourth  of  an  inch  in  diameter ;  and  sup- 
pose, further,  that  over  the  back  of  that  dermal  sac  which 
forms  the  eye,  these  meshes  are  so  small  that  a  microscope 


26  THE    TATA   OF    PSYCHOLOGY. 

is  re(![uired  to  distinguisli  tliem.  Having  imagined  sucli  a 
net-work  of  wliicli  tlic  meslicsj  irregularly  polygonal  in 
their  outlines^  are  thus  wide  over  parts  of  the  surface  that 
have  but  little  variety  of  converse  with  the  external  world, 
and  become  smaller  in  proportion  as  the  surfaces  have 
multiplied  and  variable  contacts  with  things  ;  we  shall  have 
gained  an  approximate  idea  of  the  relations  among  the 
separate  local  areas  in  which  there  arise  independent  nerves. 
To  complete  the  conception,  however,  something  else  must 
•be  supposed.  The  large  meshes  we  must  represent  as 
marked  out  by  very  broad  lines — say  a  quarter  of  an  inch 
broad  where  the  meshes  are  largest.  We  must  imagine 
them  narrowing  as  the  meshes  become  smaller;  until, 
when  we  come  to  the  meshes  over  the  surface  of  the 
retina,  the  dividing  lines  have  dwindled  to  the  thick- 
ness of  a  gossamer  thread.  And  now  let  us  conceive  that 
within  each  of  these  areas,  large  or  small  as  it  may  happen, 
there  exists  a  plexus  of  fibres,  formed  of  the  essential  nei've 
substance,  that  are  continuous  with  one  another,  but  have 
no  connection  with  the  fibres  occupying  adjacent  areas. 
Not,  indeed,  that  we  must  conceive  any  sharp  limitation  of 
the  space  occupied  by  each  plexus.  We  must  assume  that 
the  line  separating  two  areas,  here  very  broad  and  here  very 
narrow,  covers  a  space  into  which  fibres  from  both  the  areas 
run,  without  joining' one  another.  Hence  the  area  belong- 
ing to  each  independent  plexus,  is  the  internal  area  of  the 
mesh,  plus  the  space  occupied  by  its  circumscribing  broad 
or  narrow  line ;  and  the  breadth  of  the  line  represents  the 
extent   to    which  adjacex^t    areas  overlap.  Such, 

then,  are  the  peripheral  expansions  of  those  nerves  which 
are  liable  to  be  acted  on  by  external  forces.  Here  each 
monopolizes  a  relatively-great  tract  of  the  surface,  and  here 
an  extremely  minute  one.  Each  is  an  independent  agent — 
each  is  capable  of  having  a  change  set  up  in  it  without 
changes  being  set  up  in  its  neighbours.  The  skin  is,  as  it 
were,  occupied  all  over  with  separate  feelers,  that  are  here 


THE    STRUCTUEE   OP   THE   NERVOUS    SYSTEM.  27 

widely  scattered,  here  clustered,  and  here  crowded  together 
as  closely  as  maintenance  of  their  individualities  will  allow. 

From  the  nerve-plexus  occupying  one  of  these  areas,  there 
takes  its  rise  the  central  fibre,  or  axis-cylinder,  of  a  nerve- 
tube.  Coated  with  its  medulla  and  inclosing  sheath,  it 
takes  its  way  from  the  surface  inwards,  and,  proceeding 
without  any  branch  or  junction,  eventually  reaches  a  mass 
of  grey  matter  with  imbedded  vesicles — a  nerve-centre  or 
ganglion.  Into  the  substance  of  this  the  essential  nerve- 
thread  runs,  becoming  divested  of  its  medullary  sheath; 
and  where  the  structure  is  least  involved,  the  essential 
nerve-fibre  frequently  if  not  always  ends  in  a  nerve-vesicle. 
In  such  simple,  and  what  we  may  call  typical,  centres,  there 
branches  out  from  some  other  part  of  the  nerve-vesicle, 
another  nerve-fibre  which,  similarly  inclosed  in  its  double 
sheath,  pursues  an  outward  course,  ordinarily  along  the 
same  general  route  as  the  first,  until,  reaching  the  same 
part  of  the  body,  it  buries  itself  in  a  bundle  of  muscular 
fibres  amid  Avhich  its  ramifications  end.  Thus  we  have  as 
the  elements  of  what  is  called  a  nervous  arc — 1,  a  peri- 
pheral expansion,  placed  where  it  is  liable  to  be  disturbed 
by  an  external  agent,  and  so  formed  as  to  be  most  easily 
disturbed;  2,  a  connected  fibre  capable  of  being  readily 
affected  by  disturbances  at  this  outer  end,  but  shielded  from 
distm'bances  elsewhere ;  3,  at,  or  near,  the  inner  end  of  this 
fibre,  a  corpuscle  of  unstably-arranged  substance,  apt  to 
give  out  much  molecular  motion  when  disturbed ;  4,  a 
second  fibre  diverging  from  the  corpuscle,  or  its  neigh- 
bourhood, and  subject  to  disturbance  from  the  molecular 
motion  disengaged  near  its  origin,  but  protected  from  other 
influences  ;  5,  at  the  remote  extremity  of  this  second  fibre, 
a  subdivided  termination  amid  a  substance  that  contracts 
greatly  when  disturbed,  and  which,  in  contracting,  moves 
the  part  of  the  body  in  which  the  first  fibre  took  its  rise, 
rig.  1  is  a  diagram  representing  these  elements  of  a  nervous 
arc :  A  being  the  first,  or,  as  it  is  called,  afierent  nerve. 


28  THE    DATA   OP   PSYCHOLOGY. 

witli  its  peripheral  expansion  a;  B  being  tlie  nerve-cor- 
puscle or  ganglion-cell ;  and  C  tlie  second,  or  eflferent, 
nerve,  with  its  termination  c. 


rig.  1.  Kg.^. 


tr^Tt  iryt/t  fita-/. 


This  arrangement  of  parts  is  perpetually  repeated  through- 
out the  nervous  system ;  and  if  we  generalize  the  concep- 
tion somewhat  by  supposing  that  the  commencement  a  is 
not  necessarily  external.,  but  may  be  on  an  inner  surface,  or 
within  an  organ,  while  the  termination  c  is  not  necessarily 
in  a  muscle  but  may  be  in  a  gland ;  we  shall  have  a  concep- 
tion that  is,  in  a  certain  sense,  universally  applicable.  I 
say  in  a  certain  sense,  because,  until  another  element  is 
added,  the  conception  is  incomplete.  These  coupled  nerves, 
with  the  ganglion-cell  acting  as  a  direct  or  indirect  link 
between  them,  recurring  everywhere  in  substantially  the 
same  relations,  appear  to  form  a  compound  structure  out 
of  which  the  nervous  system  is  built — its  unit  of  comjDosi- 
tion.  But  this  is  not  so.  By  multiplication  of  such  arcs 
we  may  get  a  multitude  of  separate  nervous  agencies, 
but  not  a  nervous  system.  To  produce  a  nervous  system 
there  needs  an  element  connecting  each  such  nervous  arc 
with  the  rest — there  needs  a  third  fibre  running  from  the 
ganglion-cell,  or  its  neighbourhood,*  to  some  place  where 
other  communicating  fibres  come ;  and  where,  by  direct  or 
indirect  junctions,  actual  or  approximate,  the  primary 
couples  of  nerves  may  be  brought  into  relation.  That  is, 
there  requires  what  we  may  call  a  ccntrij)ctal  nerve.*     In 

*  The  words  centripetal  and  centrifugal  are  occasionally  used  in  nerve- 
physiology  as  the  equivalents  of  afferent  and  efferent.  But  as  afferent  and 
efferent  are  by  far  the  most  generally  adopted,  and  are  also  the  most  descrip- 
tive, it  seems  to  me  that  the  word  ccntripctcd  may  with  advantage  have  this 
more  special  meaning  given  to  it ;  and  centrifugal  the  correlative  meaning. 


THE    STRUCTURE    OF    THE    NERVOUS    SYSTEM. 


29 


Fig.  2  is  shown,  diagrammatically,  the  relation  in  which 
this  stands  to  the  others.  A  centripetal  nerve  being  added, 
there  results  what  we  may  fairly  regard  as  the  unit  of  com- 
position of  the  nervous  system.  We  shall  have  presently 
to  recognize  certain  fibres  which  this  conception  does  not 
include.  But  they  are  not  essential ;  for  a  nervous  system 
is  possible  without  them.  Let  us,  then,  taking  this  as  our 
unit  of  composition,  consider  the  general  method  after  which 
a  nervous  system  is  constructed. 


§  11.  The  fibres  represented  in  the  above  diagrams,  do 
not  ordinarily  pursue  their  respective  courses  by  themselves  : 
they  proceed  in  company,  as  shown  in  Fig.  3.  The  afferent 
nerves  arising  at  a,  in  separate  but  adjacent  areas  on  the 
skin,  or  in  other  organs  recipient  of  external  impressions, 
converge ;  and,  while  maintaining  their  separate  indivi- 
dualities, become  united  into  a  bundle  inclosed  in  a  sheath. 


Other  sheathed  bundles  of  fibres  from  other  clustered  areas 
in  the  same  region,  presently  join  them,  and  run  along  with 
theni  in  a  compound  bundle,  until  they  eventually  reach  the 
mass  of  imbedded  nerve-vesicles  constituting  a  ganglion  or 
nervous  centre  B.  Similarly  the  efierent  nerves  which  have 
their  roots  in  this  ganglion,  issue  from  it  as  a  bundle,  which, 
commonly  inclosed  in  the  same  general  sheath  as  the  afferent 
nerves,  goes  back  to  the  part  of  the  body  whence  these 
arose ;  and  secondary  bundles  of  these  efferent  nerves, 
diverging  and  re-diverging  from  one  another  as  they  enter 
this  part,  as  at  c,  finally  become  lost  in  its  various  muscles. 


30  THE   DATA   OF   PSYCHOLOGY. 

Ill  like  manner  tlie  centripetal  fibres  d,  originating  in  tliis 
ganglion,  take  tlieir  common  course,  joined  perhaps  by  otlier 
fibres  originating  elsewhere,  towards  a  ganglion  E,  that  is 
larger  and  has  more  numerous  connections.  Of  course  the 
clustered  lines  and  spotted  circles  in  Fig.  3,  are  entirely 
diagrammatic — give  no  idea  of  the  separate  nerves  and 
bundles  and  ganglia  as  they  actually  exist;  but  merely  of  the 
relations  in  which  they  stand  to  one  another.  It  should  be 
added  that  the  more  central  ganglion,  to  which  converge 
other  bundles  of  centripetal  nerves  (together  w'ith  some 
afferent  nerves  that  pass  through  inferior  ganglia  without 
stopping)  may  itself  be  subordinate  to  a  still  superior,  or 
still  more  central,  ganglion.  To  this  it  gives  off  what  may 
be  called  superior  centripetal  nerves  ;  and  other  nei-^-es  of 
the  same  or  of  a  lower  order  being  brought  to  it,  this  highest 
ganglion  becomes  a  place  where  there  are  established 
communications  among  all  the  subordinate  and  sub-subordi- 
nate ganglia,  with  their  afferent  and  efferent  fibres. 

One  further  kind  of  connection  exists.  The  immense 
majority  of  animals,  have  their  parts  symmetrically  arranged 
— sometimes  radially  but  more  frequently  bi-laterally.  For 
the  corresponding  parts  there  are  habitually  cori-esponding 
e-ano-lia  ;  and  the  connections  that  remain  to  be  named  are 
those  between  these  corresponding  ganglia,  or  ganglia  which 
belong  to  the  same  grade.  Such  connections  consist  of 
what  are  called  commissural  fibres.  They  are  indicated  at  h, 
where  they  transversely  join  the  structure  shown  in  detail, 
with  the  answering  structure  belonging  to  the  other  side  of 
the  body.  The  word  commissural  is,  indeed,  sometimes 
used  in  a  wider  sense  :  including  fibres  that  unite  ganglia  of 
different  grades.  But  since  the  great  majority  of  the  liljres 
called  commissural  are  those  wdiich  join  duplicate  ganglia,  or 
else  ganglia  that  occupy  like  relations  in  the  hierarch}^,  it 
will,  I  think,  conduce  to  clearness  to  restrict  its  application 
to  these :  leaving  the  word  centripetal  for  fibres  Avliich  con- 
nect ganglia  of  lower  orders  with  those  of  higher  orders. 


THE  STRUCTURE  Or  THE  NERVOUS  SYSTEM.        31 

The  commissures  thus  bringing  into  relation  the  members  of 
each  pair  of  centres^  inferior  or  superior^  and  so  linking  the 
two  halves  of  the  nervous  system,  complete  the  nervous 
communications  throughout  the  organism. 

This  description,  purposely  generalized  with  a  view  of 
exhibiting  the  principles  of  nervous  organization,  apart 
from  any  particular  type,  may  be  fitly  supplemented  by  the 
description  of  a  special  structure  that  illustrates  them. 
Each  sucker  on  any  arm  of  a  cuttle-fish,  has  a  ganglion 
seated  beneath  it.  To  this  descend  the  afierent  nerves  that 
are  afiected  by  touching  the  sucker ;  and  from  it  ascend  the 
eflerent  nerves  distributed  to  the  muscular  fibres  of  the 
sucker.  These  form  a  local  nervous  system  that  is  ex- 
perimentally proved  to  have  a  certain  completeness  in  itself. 
But  now  from  the  ganglion  underneath  each  sucker,  fibres 
run  along  the  arm,  in  company  with  fibres  from  all  similar 
ganglia  in  the  arm ;  and  this  bundle  of  centripetal  fibres 
eventually  reaches  a  ganglion  at  the  base  of  the  arm.  Each 
arm,  similarly  constructed,  thus  has  a  chief  nervous  centre 
in  which  the  fibres  from  all  its  minor  nervous  centres  are 
brought  into  communication.  Further,  all  round  the  ring 
formed  by  the  united  base  of  the  arms,  there  runs  an  an- 
nular commissure  connecting  these  superior  ganglia.  And 
then  from  each  of  them  is  given  off  a  bundle  of  fibres  that 
proceed  centripetally  to  a  still  higher  centre — the  cephalic 
ganglion ;  where,  consequently,  nerves  from  all  the  arms  are 
brought  into  dii-ect  communication  with  one  another,  and 
also  into  communication  with  nerves  arriving  from  ganglia 
in  other  parts  of  the  body.  Omitting  details  and  qualifica- 
tions, not  essential  to  such  a  conception  as  concerns  us  here, 
we  thus  see  that  in  nervous  structure  there  is  a  centraliza- 
tion and  re- centralization,  that  is  carried  far  in  proportion 
as  the  oro-anization  is  hi^h. 

§  12.  We  may  be  sure  that  along  with  a  jDrinciple  of  ar- 
rangement among  connecting  structures,  there  goes  some 


82  THE    DATA   OF   PSYCHOLOGY. 

l^rinciple  of  composition  in  tlie  centres  that  are  connected  ; 
whicli  are  not  simply  places  for  tlie  meeting  of  fibres^  but 
places  in  wliicli  there  exist  agents  liable  to  be  acted  on  by 
the  in-comiiig-  fibres  and  capable  of  acting  on  the  out -going 
fibres.  Respecting  the  principle  of  composition,  our  reason- 
ings must  be  mainly  hypothetical ;  but  they  will,  I  think, 
prove  of  some  worth,  by  leading  us  to  conclusions  that  har- 
monize with  observation,  so  far  as  this  carries  us. 

In  ascending  from  the  lowest  to  the  highest  types  of  the 
nervous  system,  we  see  that  the  distribution  and  •combi- 
nation of  nerve-fibres  are  so  modified,  as  to  make  possible  an 
increasing  multiplicity,  variety,  and  complexity  of  relations 
among  diSerent  parts  of  the  organism.  What  kind  of  mo- 
dification does  this  necessitate  at  places  where  the  nerve- 
fibres  are  put  in  communication  ?  Without  assuming  that 
two  fibres  which  bring  two  parts  of  the  organism  into  rela- 
tion, are  always  united  at  their  central  extremities  by  an 
intermediate  nerve-corpuscle,  it  may  be  safely  assumed  that 
continuity  between  their  central  extremities  must  be  eSected 
either  by  a  nerve-corpuscle  or  by  some  less-defined  portion 
of  grey  substance  ;  and  it  is  clear  that  in  proportion  to  the 
number  of  different  connections  to  be  established  among  the 
nerves  coming  to  any  ganglion,  must  be  the  number  of  th^ 
more  or  less  independent  portions  of  grey  substance  re- 
quired to  establish  them.  Let  us  consider  the  implications. 
Suppose  that  a  and  h,  Fig.  4,  are  two  points  in  the  or- 
ganism. To  join  the  nerves  proceeding  from  them,  there 
nerds  only  the  single  ganglion-cell  A.  Similarly,  to  bring 
into  nervous  relation  the  points  c  and  d,  the  single  ganglion- 
cell  B  suffices.  So  long  as  A  and  B  remain  unconnected, 
these  two  simple  relations  are  the  only  possible  ones  among 
the  points  a,  h,  c,  d.  But  now  assume  that  from  A  and  B 
there  run  fibres  to  the  centre  C — not  a  single  fibre  from 
each,  but  two  fibres,  one  of  which  in  each  case  proceeds  from 
a  or  h,  and  from  c  or  d.  This  being  so,  there  may  be  formed 
at  C,  eleven  simple  and  compound  relations :    these  four 


THE    STRUCTURE    OF   THE    NERVOUS    SYSTEM. 


33 


points  can  be  arranged  into  six  groups  of  two,  a  h,  a  c,  a  d, 
he,  h  d,  c  d  ;  into  four  groups  of  three,  h  a  c,h  a  d,  a  c  d,  c  h  d; 
and  into  one  group  of  four,  a  h  c  d.  Hence,  supposing  tlie 
centre  C  to  be  made  up  of  tlie  independent  cells,  or  portions 
of  grey  substance,  severally  serving  to  link  tlio  members  of 
a  group  into  a  separate  combination,  there  must  be  at 
least  eleven  such.  If,  again,  from  this  centre  C,  we  assume 
that  there  run  adequately  numerous  fibres  to  the  higher 
centre  F,  and  that  this  is  also  duly  connected  through 
the  centres  D  and  E,  with  the  points  e,  f,  g,  li ;  then 
the  possible  number  of  groups,  simple  and  compound, 
that  may  be  formed  at  F,  will  amount  to  247 ;  and  to 
unite  the  members  of  each  group  so  that  it  may  be  inde- 
pendent of  the  rest,  there  must  be  at  least  247  connect- 


ing  links  at  the  centre  F.  Without  pursuing  the  calcu- 
lation, it  will  be  manifest  that  as  these  points  in  the  or- 
ganism increase  in  number,  and  as  the  clusters  of  them 
that  are  to  be  brought  into  relation  become  larger  and  more 
various,  the  central  elements  through  which  their  relations 
are  established  must  grow  multitudinous.  An  in- 

adequate conception,  however,  is  thus  reached ;  for  we  have 
considered  only  the  requisites  for  forming  among  these 
points,  the  greatest  numher  of  different  groups,  simple  and 
compound;  ignoring  the  different  orders  in  which  the 
3 


84  THE    DATA   OP   PSYCHOLOGY. 

members  of  eacli  group  may  be  combined.  Two  tilings  can 
be  arranged  in  succession  in  only  2  different  ways ;  tlire<i 
things  can  be  arranged  in  6  different  ways ;  four  tbings  in 
24  ways  ;  five  tilings  in  120  ways  ;  six  tilings  in  720  ways; 
seven  things  in  5^040  ways ;  and  so  on  in  a  progression 
increasing  witli  enormous  rapidity.  Assuming,  tlieii,  that 
at  the  centre  F,  certain  points,  a,  h.  c,  d,  e,  are  to  be  com- 
bined, not  in  this  succession  only,  but  in  all  possible  suc- 
cessions, there  Avill  require  120  different  links  of  connec- 
tion for  this  one  group  of  five  points  only.  These  links, 
whether  separate  vesicles  or  less-differentiated  portions  of 
grey  matter,  must  occupy  a  considerable  space ;  and  sup- 
posing they  are  aggregated  near  those  pre-existing  cells 
or  links  which  they  have  to  re-combine  in  various  orders, 
there  may  result  a  protuberance  from  the  centre  F,  as  shown 
at  G.  If  we  suppose  that  instead  of  a  group  of  five,  a  group 
of  six  is  to  have  its  members  thus  variously  combined; 
or  if  instead  of  one  group  to  be  so  dealt  with,  there  are 
many ;  this  lateral  outgrowth  may  become  relatively  very 
large.  And  since  its  vesicles,  or  portions  of  grey  matter, 
will  be  much  more  bulky  than  the  fibres  running  from  them 
to  the  members  of  groups  which  they  combine,  there  may' 
be  expected  to  arise,  as  at  H,  a  lateral  centre  attached  to 
the  original  centre,  F,  by  a  pedicle  of  fibres. 

Of  course  these  diagrams  and  numbers  are  intended  to 
convey  nothing  but  a  general  idea  of  the  principle  of  com- 
position of  nerve  centres — not  to  represent  any  actual  com- 
position. It  would  be  an  absurd  assumption  that  among  a 
number  of  points  in  the  body,  there  have  to  be  formed  as 
many  unlike  groups  as  are  theoretically  possible ;  and  it  is 
not  to  be  supposed  that  the  members  of  any  group  need 
ever  to  be  combined  in  as  many  different  orders  as  they 
might  be  combined.  But  while,  on  the  one  hand,  the  above 
description  greatly  over-states  the  accumulation  of  nerve- 
vesicles,  or  their  equivalents,  implied  by  such  correlations  as 
are  actually  required  among  a  given  number  of  points  in  the 


THE  STRUCTURE  OP  THE  NERVOUS  SYSTEM.        35 

organism  ;  it  immensely  under-states  the  number  of  points 
to  be  so  correlated,  as  well  as  tlie  number,  and  variety,  and 
complexity,  of  the  groups  into  which  they  are  to  be  com- 
bined. The  places  from  which  afferent  nerves  proceed,  as 
well  as  the  places  to  which  efferent  nerves  pi'oceed,  are 
multitudinous.  Very  large  groups  of  such  places  have  their 
members  put  in  simultaneous  communication.  The  different 
groups  so  formed  are  innumerable.  And  extremely  varied 
relations  of  succession  are  established  among  members  of 
the  same  group  ;  as  well  as  among  different  groups.  Hence 
we  are  safe  in  asserting  that  along  with  an  increasing  multi- 
plicity and  heterogeneity  of  nervous  connections,  there  must 
go  increasing  massiveness  of  the  nervous  centres,  or  accu- 
mulations of  vesicular  matter. 

One  further  corollary  deserves  noting.  Each  vesicle,  or 
each  portion  of  grey  matter  that  establishes  a  continuity 
between  the  central  termini  of  fibres,  is  not  merely  a  con- 
necting link  :  it  is  also  a  reservoir  of  molecular  motion,  which 
it  gives  out  when  disturbed.  Hence,  if  the  composition  of 
nerve-centres  is  determined  as  above  indicated,  it  follows 
that  in  proportion  to  the  number,  extensiveness,  and  com- 
plexity, of  the  relations,  simultaneous  and  successive,  that 
are  formed  among  different  parts  of  the  organism,  will  be 
the  quantity  of  molecular  motion  which  the  nerve-centres 
are  capable  of  disengaging. 

§  13.  As  a  datum  for  Psychology  of  the  most  general 
kind,  the  foregoing  description  of  nervous  structure  might 
suffice.  But  having  to  deal  chiefly  with  that  more  special 
Psychology  distinguished  as  human,  it  will  be  proper  to  add 
some  account  of  the  human  nervous  system.  A  few  facts  of 
moment  respecting  its  peripheral  parts,  may  be  set  down 
before  we  study  its  central  parts. 

At  the  surface  of  the  body,  where  the  extremities  of 
nerve-fibres  are  so  placed  as  to  be  most  easily  disturbed,  we 
generally  find  what  may  be  called  multipliers  of   distur- 


36  THE    DATA   OP    PSYCnOLOGY. 

bances.  Sundry  appliances  wliicli  appear  to  liavc  notliing  in 
common,  liave  the  common  function  of  concentrating,  on  tlie 
ends  of  nerves,  the  actions 'of  external  agents.  That  this  is 
the  effect  produced  by  the  lenses  of  the  eyes,  is  a  familiar 
Cict.  It  is  a  less  familiar  fact  that  certain  otolites  and 
minute  rods  or  fibres,  immersed  in  a  liquid  contained  in  the 
internal  ear,  serve  to  transform  the  less  sensible  vibrations 
communicated  to  this  liquid,  into  the  more  sensible  vibrations 
of  solid  masses,  and  to  bring  these  directly  to  bear  on  the 
nerve-terminations.  So,  too,  is  it  over  the  integument;  or, 
at  any  rate,  over  the  parts  of  it  subject  to  many  and  varied 
contacts.  Though  men  have  not,  like  many  inferior  Mam- 
mals, the  well-developed  tactual  multipliers  called  vihrissce 
(known  in  a  cat  as  "'whiskers"),  each  of  which  is  a  lever 
that  intensifies  a  slight  touch  at  the  outer  end  into  a  strong 
pressure  of  the  imbedded  end  upon  an  adjacent  nerve-fibre ; 
yet  every  one  of  the  short  hairs  on  a  man's  skin  acts  in  the 
same  way.  And  then,  in  addition  to  these,  there  are,  at 
places  where  the  contacts  Avith  objects  are  perpetual,  and 
where  hairs  do  not  grow,  certain  multipliers  below  the  sur- 
face— small  dense  bodies  named  corpnscuJa  tadns,  round  each 
of  which  a  nerve-fibre  ramifies,  and  each  of  which,  when 
moved  by  the  touch  of  a  foreign  body,  gives  to  its  attached 
nerve-fibre  a  greater  pressure  than  this  would  receive  were 
the  surrounding  substance  homogeneous :  a  fact  which  Avill 
be  understood  on  remembering  the  effect  of  pressure  on  the 
skin  when  some  small  hard  body,  as  a  thorn,  is  imbedded 
in  it. 

So  much  for  the  instruments  that  are  external  to  the 
peripheral  expansions  of  the  nerves,  and  serve  to  exag- 
gerate the  effects  of  incident  forces.  We  may  now  con- 
template these  peripheral  expansions  themselves,  as  being 
adapted  to  receive  these  exaggerated  incident  forces. 
In  the  first  place,  the  ultimate  nerve-fibrillD3,  ramifying 
where  they  are  most  exposed  to  disturbances,  consist  of 
nerve-protoplasm  unprotected  by  medullary  sheaths  and  not 


THE    STRUCTUUE    OP   THE   NERVOUS    SYSTEM.  37 

even  covered  by  membranous  slieatlis.  In  fact,  tliey  appear 
to  consist  of  matter  like  tliat  contained  in  nerve-vesicles, 
but  without  the  fat-granules ;  and  may  be  regarded  as,  like 
it,  more  unstable  than  the  matter  composing  the  central 
fibres  of  the  fully-differentiated  nerve-tubes.  To  this  general 
character  of  the  nerve-terminations,  have  to  be  added  the 
more  special  characters  of  the  terminations  exposed  to 
special  forces.  The  delicate  pale  fibres  which  form  a  layer 
on  the  surface  of  the  retina,  are  not  directly  affected  by  the 
rays  of  light  concentrated  upon  them ;  but  these  rays,  pass- 
ing through  them,  fall  on  a  layer  of  closely  packed,  but  quite 
separate,  little  bodies  which  are  the  true  sensitive  structures ; 
and  then  the  minute  nerve-fibrillee  that  run  from  these  to 
the  stratum  of  retinal  nerve-fibres,  pass  on  their  way  into  a 
layer  of  nerve- vesicles,  with  which  we  may  presume 
they  have  connections.  That  is  to  say,  this  peripheral 
expansion  of  the  nerve  on  which  visual  images  fall, 
contains  numerous  small  portions  of  the  highly-unstable 
nerve-matter,  ready  to  change,  and  ready  to  give  out 
molecular  motion  in  changing.  It  is  thus,  too,  with 
those  terminal  ramifications  of  the  auditory  nerve,  on  which 
sonorous  vibrations  are  concentrated.  And  there  is  an 
analogous  peculiarity  in  the  immensely-expanded  extremity 
of  the  olfactory  nerve.  Here,  over  a  large  tract  covered 
by  mucous  membrane,  is  a  thick  plexus  of  the  grey  un- 
sheathed fibres ;  and  among  them  are  distributed  both 
nerve-vesicles  and  granular  grey  substance,  such  as  that  out 
of  which  the  vesicles  arise  in  the  nervous  centres. 

The  significance  of  these  structural  peculiarities  we  shall 
see  hereafter.  For  the  present  we  need  only  note  the  distri- 
bution of  them.  Over  the  skin,  which  is  conversant  with 
forces  of  a  relatively-considerable  intensity — mechanical 
impacts,  pressures,  tensions, — we  do  not  find  that  the  nerve- 
terminations  contain  deposits  of  the  peculiarly  unstable 
nerve-substance.  But  we  find  such  deposits  where  the 
incident  forces  are  extremely  feeble,  or  fall  on  excessively 


38  THE    DATA   OF   PSYCIIOLOaY. 

small  areas,  or  both.  The  quantity  of  matter  which,  floating 
as  faint  odour  through  the  air,  reaches  the  end  of  the  ol- 
factory nerve,  is  infinitesimal.  Such  luminiferous  undula- 
tions as  are  allowed,  during  a  momentary  glance,  to  fall  on 
one  of  the  minute  areas  of  the  retina,  arc  equivalent  to  a 
mechanical  force  inappreciable  by  our  measures,  if  not  in- 
expressible by  our  figures.  Similarly  with  those  atmo- 
spheric waves  which,  produced  by  the  church-bell  a  mile 
away,  and  weakening  as  they  spread  in  all  directions,  are 
conveyed  to  the  minute  otolites  and  rods  of  the  inner  ear, 
to  be  by  them  impressed  on  the  auditory  nerves.  And  in 
these  places  it  is  that  we  find  peripheral  deposits  of  the 
specially-unstable  nerve-substance. 

§  14.  Arising  from  these  variously-specialized  peripheral 
structures,  the  afferent  nerves,  collected  into  their  bundles 
and  compound  bundles,  run  inwards  to  the  spinal  cord ;  out 
of  which  issue  the  corresponding  bundles  of  efferent  nerves. 
In  one  sense  the  spinal  cord  may  be  regarded  as  a  con- 
tinuous nervous  centre ;  and,  in  another  sense,  as  a  series  of 
partially-independent  nervous  centres.  Each  pair  of  trunk 
nerves  with  its  segment  of  the  spinal  cord,  has  a  certain 
degree  of  individuality;  and  those  segments  into  which 
enter  the  pairs  of  massive  nerves  from  the  limbs,  have 
individualities  considerably  pronounced ;  since  it  is  experi- 
mentally proved  that  when  severed  from  the  rest  they  are 
not  incapacitated.  The  tract  of  grey  matter  in  the  spinal 
cord  to  which  the  afferent  nerves  of  a  limb  come,  and  from 
which  the  efferent  nerves  issue,  is  practically  the  ganglionic 
centre  of  that  limb,  having  very  much  of  automatic  inde- 
pendence ;  and  being  joined  by  commissural  fibres  to  a 
like  centre  belonging,  to  the  fellow  limb,  it  forms  with  this 
an  automatic  pair.  So  that,  remembering  how  the  entire 
cranio-spinal  axis  is  originally  one  and  continuoiis,  and  that 
its  anterior  part  has  been  differentiated  and  developed  into 
quite  distinct  centres  we  may  say  that  its  posterior  part,  the 


THE  STRUCTURE  OP  THE  NERVOUS  SYSTEM.        89 

spinal  cord,  lias  also  been  so  differentiated,  tliough  to  a 
much   smaller    extent.  To    tliis    conception    two 

additions  must  be  made.  Beyond  the  internal  tracts  of  grey 
or  vesicular  matter,  and  the  bundles  of  nerve-fibres  that 
enter  into  and  issue  from  them  laterally ;  and  beyond  the 
Iran  verse  commissural  fibres  which  connect  the  corresponding 
lateral  portions  of  grey  matter  or  partially-differentiated 
pairs  of  nervous  centres ;  there  are  longitudinal  commissural 
fibres,  joining  these  successive  pairs  of  nervous  centres  Avith 
one  another,  and  serving  to  integi'ate  the  series  of  j)airs  in 
the  same  way  that  the  members  of  each  pair  are  integrated. 
And  then,  along  with  these  fibres  that  unite  nervous  centres 
of  the  same  order,  there  are  what  we  found  it  desirable  to 
distinguish  as  centripetal  fibres,  running  from  the  relatively- 
inferior  nervous  centres  to  the  relatively-superior  ones  ; 
with  centrifugal  fibres  running  back. 

Of  these  relatively-superior  nervous  centres,  %ve  have  first 
to  notice  the  medulla  oblongata  f  including  those  parts 
of  the  2^ons  Varolii  which  are  woven  into  it,  and  similarl}^ 
arise  out  of  the  fourth  ventricle.  This  is  the  enlarged 
termination  of  the  spinal  cord,  lying  within  the  skull. 
Distinguished  as  it  is  from  lower  parts  of  the  spinal  cord  by 
its  greater  massiveness,  it  is  much  more  distinguished  by  the 
multiplicity  and  variety  of  its  peripheral  connections. 
While  the  successive  segments  of  the  spinal  cord  proper, 
have  pairs  of  afferent  and  efferent  nerves  which  are  limited 
in  their  distributions  to  particular  regions  of  the  body  ;  and 
while  even  such  an  entire  group  of  these  segments 
as  occupy  the  lumbar  region,  have  relations  only  with 
the  legs  and  the  lower  part  of  the  body;  the  medulla 
oblongata,  by  the  intermediation  of  centripetal  fibres,  is 
brought  into  relation  not  only  with  the  lower  part  of  the 
body  and  its  limbs,  but  with  the  upper  part  of  the  body  and 
its  limbs  ;  and  not  only  with  these,  but  also  with  sundry  of 
the  parts  which  we  know  as  the  organs  of  the  special  senses  ; 
and  not  only  wath  these,  but  also  with  the  more  important 


40  THE    DATA   OF   PSYCHOLOGY. 

viscera.  The  auditory  nerves  and  the  nerves  of  taste  go 
directly  into  it,  and  though  the  optic  nerves  do  not,  yet 
from  the  centres  to  which  they  run  there  are  fibres  communica- 
ting with  it;  from  its  laterally-appended  parts  arise  the 
nerves  of  the  eye-muscles  and  the  facial  nerves ;  and  the 
pneumogastric  nerves,  given  off  from  its  posterior  part,  put 
it  in  communication  with  the  larynx,  the  lungs,  the  heart, 
the  liver,  and  the  stomach.  Respecting  its  connections,  direct 
and  indirect,  much  remains  to  be  ascertained ;  but  what  is 
known  justifies  the  conclusion  that  the  medulla  oblongata, 
including  the  structures  that  are  adnate,  is  a  portion 
of  the  originally-uniform  cerebro-spinal  axis,  which  has 
been  differentiated  into  a  centre  of  a  higher  order  than 
those  behind  it,  or  those  at  the  base  of  the  mass  in  front 
of  it — higher  in  the  sense  that  it  has  become  that  portion 
of  the  axis  in  which  centripetal  fibres  running  from  the 
posterior  ganglia,  and  from  some,  if  not  all,  of  the  anterior 
ganglia,  called  by  some  sensory,  are  brought  into  relation 
with  one  another — a  centre  through  which  these  local 
centres  are  united  into  one  system. 

Passing  over  with  a  mere  recognition  the  anterior  ganglia 
just  named,  the  exact  relations  of  which  are  ill-understood, 
but  some  of  which  comparative  morphology  proves  to  be 
portions  of  the  front  end  of  the  cerebro-spinal  axis  that 
have  become  differentiated  into  ganglia  of  the  first  order, 
receiving  those  special  external  stimuli  to  which  the  front 
end  of  the  body  is  exposed ;  there  remain  only  to  be  noticed 
the  two  great  bi-lobed  ganglia,  which  in  Man  form  the  chief 
mass  of  the  brain — the  cerebellum  and  the  cerebrum.  Phy- 
siologists and  anatomists  are  agreed  in  regarding  these  as 
centres  of  a  still  higher  order.  Anatomical  proof  of  their 
superiority,  as  being  the  seats  of  still  higher  centralization, 
is  very  incomplete  ;  for  the  difficulty  of  tracing  the  courses 
of  all  the  nerve-fibres  that  enter  into  and  issue  from  them, 
has  hitherto  been  insuperable.  But  their  connections  with 
the  subjacent  minor  centres  and  with  the  medulla  oblongata, 


THE    STKUCTUEE    OP   THE   NERVOUS    SYSTEM.  41 

are  such  as  to  make  it  certain  that  through  the  intermedia- 
tiou  of  tliese,  they  communicate  with  the  Avhole  jDeripheral 
nervous  system  ;  and  are  places  in  which  centripetal  fibres 
from  centres  of  both  the  first  and  second  orders,  joined, 
possibly,  with  some  simply  afferent  fibres,  are  brought  into 
various  relations :  relations,  however,  that  most  likely  difier 
in  their  natures  from  those  established  in  inferior  centres — 
difier,  perhaps,  as  those  supposed  to  be  formed  in  the 
centre  H,  Fig.  4,  difier  from  those  formed  in  the  centre  F. 

Among  the  facts  of  fundamental  significance  with  which 
we  are  here  concerned,  one  other  may  be  named.  This 
concerns  the  histological  structures  of  nervous  centres.  lu 
automatic  ganglia,  the  direct  union  of  nerve-fibres  with  nerve- 
cells  is  habitual.  Throughout  the  spinal  cord  the  "  axis-cylin- 
ders "  may  not  unfrequently  be  traced  running  into  the 
vesicles.  But  in  the  higher  nerve-centres  direct  connections 
are  much  less  readily  made  out;  and  it  is  question- 
able whether  in  the  highest  they  occur  at  all.  In  the 
grey  substance  of  the  cerebrum,  the  delicate  nerve-fibres 
which,  divested  of  medullary  sheaths,  run  among  the  im- 
bedded corpuscles,  do  not  directly  unite  with  them;  or  if  it  is 
too  much  to  say  that  there  are  no  such  unions,  we  may  say 
that  they  are  rare.  Such  communications  as  exist  are 
apparently  between  the  branched  terminations  of  the  fibres 
and  the  ramified  processes  of  the  corpuscles.  Thus  at  the 
one  extreme,  simple,  clear,  and  complete  connections  are 
the  rule ;  and  at  the  other  extreme,  involved,  vague,  and 
incomplete  connections. 

§  15.  Some  account  must  be  given  of  certain  remaining 
nervous  structures,  with  which  Psychology  is  indirectly 
concerned.  Thus  far  we  have  dealt  only  with  the  fibres  and 
centres  that  stand  passively  and  actively  related  to  the  ex- 
ternal world ;  but  there  are  fibres  and  centres  that  stand 
related  to  those  internal  organs  which  make  possible  the 
continuance  of  relations  to  the  external  world. 


42  THE    DATA   OF    PSYCHOLOGY. 

The  first  to  claim  attention  are  tlie  vaso-motor  nerves.  Bun- 
dles of  tliese  issue  from  the  spinal  cord,  and,  joined  by  bundle's 
of  nerves  arising  from  the  sympathetic  system,  accompany  the 
main  arteries :  dividing  and  subdividing  wherever  these  do, 
so  as  to  supply  fibres  to  all  their  branches  down  to  the  most 
minute.  The  vaso-motor  nerves  form,  in  fact,  an  additional 
scries  of  efferent  nerves.  The  nervous  arc  under  its  lowest 
form,  consists  of  the  afferent  nerve  with  its  peripheral  ex- 
tremity exposed  to  extei'nal  actions,  the  ganglion-corpuscle 
to  which  its  centi'al  extremity  runs,  and  the  efferent  nerve 
thence  issuing  to  end  in  some  muscle.  But  as  we  have 
seen,  the  unit  of  composition  of  the  developed  nervous 
system,  includes  a  centripetal  fibre,  running  from  the  first 
or  subordinate  centre  to  a  higher  centre;  and  here  we 
have  to  add,  as  an  habitual  element  of  this  unit  of 
composition  in  its  complete  form,  a  vaso-motor  fibre, 
running  to  that  part  of  the  body  in  which  the  two  ends 
of  the  nervous  arc  lie,  and  bringing  the  blood-vessels 
of  that  part  into  relation  with  the  other  parts  of  the 
apparatus. 

The  cerebro-spinal  nervous  system,  besides  ha\'ing  these 
direct  communications  with  the  muscular  walls  of  the  tubes 
which  bring  blood,  both  to  itself  and  to  the  muscles  it  sends 
fibres  to,  is  also  put  into  relation  with  other  parts  on 
which  it  is  equally,  though  less  immediately,  dependent — 
the  viscera.  These  have,  indeed,  a  nervous  system  of  their 
own,  possessing  apparently  a  considerable  degree  of  inde- 
pendence— the  sympathetic  system;  and  one  all-important 
viscus,  the  heart,  has  a  nervous  system  that  is  demonstrably 
independent.  The  morphological  interpretation  of  the  vis- 
ceral nervous  system  is  not  settled;  but  whether  it  has  a 
separate  origin,  or  belongs  to  the  periphery  of  the  cerebro- 
spinal system,  the  undoubted  fact  is  that  the  cerebro-spinal 
system,  through  the  nei-ves  running  from  it  into  the 
trunks  of  the  sympathetic,  communicates  with  all  these  vital 
organs;  and  that  even  the  heart,  complete  as  is  its  local 


THE    STRUCTURE   OF   THE    NERVOUS    SYSTESI 


nervous  system,  is,  by  the  vagus  or  pneumogastric  nerve, 
integrated  witli  the  cerebro-spinal  system. 

A  more  particular  account  of  these  and  sundry  structures 
of  the  same  class  is  not  necessary  here.  The  general  fact  of 
significance  for  us,  is,  that  the  brain  and  sjiinal  cord  which 
through  their  afferent  nerves  are  put  in  relation  with  the 
actions  of  the  external  world,  and  Avhich  through  their 
efferent  nerves  are  put  in  relation  with  the  structures  that 
react  on  the  external  world,  are  also  put  in  relation  with 
the  organs  immediately  or  remotely  instrumental  in  supply- 
ing them  with  nutriment,  and  removing  the  effete  matters 
resulting  from  their  activities. 

§  16.  In  the  foregoing  description  I  have  endeavoured  to 
include  all  that  Psychology  needs.  Many  conspicuous 
traits  of  nervous  structure  which  some  will  think  ought  to 
be  set  down,  are  really  altogether  irrelevant.  That  in  the 
spinal  cord  the  grey  matter  is  placed  internally,  while  in  the 
cerebrum  it  forms  an  outside  stratum,  is  a  fact  of  moment 
in  anatomy,  but  one  which  throws  no  light  on  the  science  of 
mind.  Knowledge  of  the  truth  that  the  posterior  roots  of 
the  spinal  nerves  are  afferent,  while  the  anterior  are  efferent, 
is  all-important  to  the  pathologist ;  but  to  the  psychologist 
it  is  quite  unimportant,  since  this  arrangement  might  have 
been  reversed  without  the  principles  of  nervous  structure 
being  in  the  least  changed ;  and  it  is  with  these  principles 
only  that  the  psychologist  is  concerned.  The  leading  facts 
embodying  these  principles  may  be  summed  up  thus  : — 

The  three  great  sub-kingdoms  of  animals  in  which  the 
nervous  system  becomes  considerably  evolved,  show  us  that 
along  with  the  relatively-increased  massiveness  distinguish- 
ing the  higher  types  of  the  nervous  system,  there  goes  that 
other  kind  of  integration  implied  by  increase  of  structural 
combination.  There  is  multiplication  and  enlargement  of 
the  parts  that  unite  local  nervous  centres  with  general 
nervous  centres.     Very  frequently  there  is  an  approach  or 


4*"  THE    DATA   OP    PSYCHOLOGY. 

clustering  of  nervous  centres  tliat  were  previously  far  apart. 
And  tliere  is  both  a  relative  and  an  absolute  increase  in 
tliose  centres  whicb  have  tlie  most  multiplied  relations  "witli 
local  centres,  and  tlirough  them  with  all  parts  of  the  body. 

The  nervous  system  is  made  up  of  threads  inclosed  in 
sheaths,  and  corpuscles  imbedded  in  protoplasm ;  of  which 
the  threads,  united  into  bundles,  constitute  almost  the  whole 
of  the  peripheral  parts,  while  the  corpuscles  with  their  matrix 
are  found  chiefly  in  the  central  parts.  Having  at  its  outer  ex- 
tremity a  plexus  of  highly-unstable  matter,  a  nerve-thread, 
consisting  as  we  conclude  of  less  unstable  matter  but 
matter  isomerically  transformed  with  ease,  runs  inwards, 
surrounded  by  substances  that  shield  it  from  lateral  distur- 
bance. Eventually  it  reaches  a  mass  of  highly  unstable 
matter,  so  conditioned  as  to  undergo  decomposition  wdth  the 
greatest  facility ;  and  from  the  place  where  this  lies  there 
run  other  like  fibres  to  other  masses  of  unstable  matter,  of 
the  same  kind,  or  of  a  different  kind,  or  both — here  to  a 
portion  of  substance  that  contracts  when  disturbed,  and 
here  to  a  superior  centre  containing  more  of  the  easily-de- 
composed nerve-substance.  These  threads,  afferent,  efferent, 
and  centripetal,  with  their  connecting  corpuscle  or  portion 
of  grey  matter,  we  regard  as  forming  the  unit  of  composition 
of  the  nervous  system. 

Such  units  are  variously  grouped  and  combined.  Each 
local  ganglion  is  a  place  where  many  afferent  and  many 
efferent  nerves  are  connected  by  many  portions  of  the  un- 
stable nerve-matter,  capable  of  suddenly  giving  out  much 
molecular  motion.  Each  superior  ganglion  is  a  place  where 
centripetal  and  centrifugal  fibres  from  such  local  or  inferior 
ganglia,  are  similarly  connected  by  similar  matter.  And  so 
with  still  higher  ganglia  in  their  relations  to  these.  From 
which  principle  of  combination  it  results  that  the  possibili- 
ties of  different  compound  relations  increase  as  fast  as  the 
centralization  progresses. 

We    saw,    however,    that    this    establishment    of    more 


'i'tiE    STBUCTURK    OP   THE    NEKVOUS 


numerous^  more  involved,  and  more  varied  relations  among 
tlic  parts  of  the  organism,  implies  not  simply  this  grouping 
of  fibres  and  this  arrangement  of  centres ;  but  also  a  mul- 
tiplication of  the  nerve-corpuscles,  or  portions  of  grey 
matter,  occupying  their  centres.  And  we  found  it  to  follow 
that  where  the  compound  relations  formed  are  among  many 
points,  or  where  the  points  are  to  be  combined  in  many  orders, 
or  both,  great  accumulations  of  grey  matter  are  needed  :  an 
important  corollary  being  that  the  quantity  of  this  matter 
capable  of  giving  out  much  motion,  increases  in  proportion 
as  the  combinations  formed  become  large  and  heterogeneous. 

Passing  to  the  special  nervous  structure  related  to  that 
special  Psychology  of  chief  importance  to  us,  we  saw 
that  the  spinal  cord  is  a  series  of  partly  de]3endent,  partly 
independent,  double  nerve-centres ;  each  concerned  with  a 
particular  portion  of  the  trunk  or  a  particular  limb,  to  the 
skin,  muscles,  and  vessels  of  which  it  sends  nerves. 
The  enlarged  cephalic  extremity  of  the  spinal  cord,  the 
medulla  oblongata,  is  a  centre  connected  by  centripetal 
fibres  with  these  partially-differentiated  inferior  centres; 
and  receiving,  as  it  also  does,  directly  or  indirectly,  nerves 
from  the  special  sense-organs,  the  medulla  oblongata  is  a 
centre  where  the  local  centres  concerned  with  nearly  all  parts 
of  the  body,  are  brought  into  communication.  We  saw,  lastly, 
that  the  two  great  bi-lobed  masses  overlying  the  medulla 
oblongata  and  the  sensory  ganglia,  with  which  they  are  in- 
timately connected,  may  be  regarded  as  centres  in  which 
these  compound  connections  are  united  into  connections  still 
more  compound,  still  more  various,  and  still  more  numerous. 

One  further  fact  which  it  remained  for  us  to  note,  was 
that  Avhile  the  more  important  nervous  structures  are  those 
which  bring  the  parts  that  are  acted  upon  by  the  outer 
world,  into  relation  with  the  parts  that  react  upon  it,  there 
are  also  nervous  structures  that  bring  all  these  into  relation 
with  the  vital  organs :  so  serving  to  unite  the  parts  which 
expend,  with  the  parts  which  accumulate  and  distribute. 


CHAPTER   III. 

THE   FUNCTIONS    OF    THE   NERVOUS    SYSTEM. 

§  17.  "VVlienj  at  tlie  outset^  we  inquired  what  are  tte 
manifestations  witli  wliicli  tlie  nervous  system  is  associated, 
we  necessarily,  in  drawing  a  conclusion,  asserted  in  general 
terms  the  part  performed  by  tlie  nervous  system.  And 
though,  in  the  chapter  just  ended  the  sole  aim  has  been 
to  describe  nerve-threads,  nerve-cells,  nerve-trunks,  nerve- 
centres,  and  the  ways  in  which  they  are  put  together ;  yet 
the  ends  subserved  have  unavoidably,  from  time  to  time, 
come  into  view.  Structure  and  function  are  in  our  thoughts 
so  intimately  related,  that  it  is  scarcely  possible  to  give  a 
rational  account  of  the  one  without  some  tacit  reference  to 
the  other.  Here,  however,  function  is  to  be  our  special 
topic.  Having  seen  how  the  nervous  system  is  constructed, 
we  have  now  to  see  how  it  Avorks. 

The  proposition  with  which  the  first  chapter  ended  was 
that  nervous  evolution  varies  partly  as  the  quantity  of 
motion  generated  in  the  organism,  and  partly  as  the  com- 
plexity of  this  motion.  Here  the  initial  inquiry  must  be, 
how  the  nervous  system  serves  as  at  once  the  agent  by  which 
motions  are  liberated  and  the  agent  by  which  motions  ai-e 
co-ordinated.  Three  things  have  to  be  explained  : — 1 .  What 
are  the  causes  which  on  appropriate  occasions  determine 
the  nervous  system  to  set  up  motion  ?     2,  By  what  process 


THE    FUNCTIONS   OP   THE   NERVOUS    SYSTEM. 


47 


does  it  liberate  tlie  insensible  motion  locked  np  in  certain 
tissues,  and  cause  its  transformation  into  sensible  motion  ? 
3.  How  does  it  adjust  sensible  motions  into  those  com- 
binations, simultaneous  and  successive,  needful  for  efficient 
action  on  tlie  external  world?  Tliese  questions  cover  the 
whole  of  its  functions ;  or,  at  any  rate,  all  those  of  its 
functions  -with  which  we  are  directly  concerned.  We  have 
to  interpret  Its  passive  function  as  a  receiver  of  disturbances 
that  set  it  going;  its  active  function  as  a  liberator  o^ 
motion ;  and  its  active  function  as  a  distributor  or  appor- 
tioucr  of  the  motion  liberated. 

Probably  it  will  be  thought  that  there  is  here  introduced 
a  function  distinct  from  those  before  named.  It  seems  that 
the  receiving  of  disturbances,  or  stimuli,  can  be  included 
neither  under  the  head  of  disengaging  motions  nor  under  the 
head  of  co-ordinating  motions.  But  on  reducing  the  facts 
to  their  lowest  terms,  and  to  those  terms  which  Physiology 
proper  can  alone  recognize,  the  difficulty  disappears.  For 
all  nervous  stimuli  are  motions,  molar  or  molecular;  and 
the'  function  of  co-ordinating  motions  comprehends  not 
simply  the  combining  and  apportioning  of  the  motions  ex- 
pended, but  also  the  combining  of  the  motions  received, 
and  the  adjustment  of  the  one  set  into  harmony  with  the 
other.  A  moment's  thought  justifies  this  proposition.  The 
stimuli  to  the  nerves  of  touch  are  sensible  motions  of  the 
imbedding  tissue,  caused  either  by  the  impacts  of  external 
moving  bodies  or  by  motions  of  the  organism  which  bring 
it  against  external  bodies,  fixed  and  moving.  The  auditory 
nerve  receives  the  motions  conveyed  to  it  from  masses  of 
matter  that  arc  vibrating.  Those  minute  agents  that  termi- 
nate the  nerves  of  the  retina  are  acted  on  by  luminiferous 
undulations — motions  of  the  ethereal  medium  which  produce 
motions  among  their  molecules.  So,  too,  tha  nerves  excited 
by  sapid  and  odorous  substances,  are,  in  fact,  excited  by  the 
molecular  movements  these  substances  cause  in  their  extre- 
mities by  chemically  changing  them.     Thus,  speaking  not 


48  THE    DATA   OF   PSYCHOLOGY. 

figuratively  but  literally,  an  afferent  fibre  of  whatever  kind 
is  a  recipient  of  motion  given  to  its  molecules :  eitlier  by 
molar  motion,  as  wlien  a  blow  is  received;  or  by  tbe 
motion  of  otlier  molecules,  as  when  there  is  contact  with 
a  chemically-active  body ;  or  by  those  ethereal  molecular 
motions  which  constitute  radiant  heat  and  light. 

It  will  be  well  to  consider  more  fully  this  sub-division 
of  nervous  functions,  and  the  reasons  for  here  proceeding 
upon  it. 

§  18.  Physiology  is  an  objective  science;  and  is  limited 
to  such  data  as  can  be  reached  by  observations  made  on 
sensible  objects.  It  cannot,  therefore,  properly  appropriate 
subjective  data ;  or  data  wholly  inaccessible  to  external 
observations.  Without  questioning  the  trath  of  the  as- 
sumed correlation  between  the  changes  which,  physically 
considered,  are  disturbances  of  nerves,  and  those  which, 
psychically  considered,  are  feelings;  it  may  be  safel}'' affirmed 
that  Physiology,  which  is  an  interpretation  of  the  physical 
processes  that  go  on  in  organisms,  in  terms  known  to 
physical  science,  ceases  to  be  Physiology  when  it  imj)orts 
into  its  interpretations  a  psychical  factor — a  factor  which 
no  physical  research  whatever  can  disclose,  or  identify,  or 
get  the  remotest  glimpse  of.  The  relations  between  nerve- 
actions  and  mental  states  form  a  distinct  subject,  to  be 
dealt  with  presently.  Here  we  are  treating  of  nerve-ac- 
tions on  tlioir  physiological  side,  and  must  ignore  their 
psychological  side. 

Doing  this,  we  have  no  alternative  but  to  formulate  them 
in  terms  of  motion.  And  having  recognized  the  primary 
division  to  be  that  between  the  liberation  of  motions  and 
the  co-ordination  of  motions,  we  find  that  this  last  division 
must  be  sub-divided.  It  includes,  first,  the  co-ordination 
of  the  motions  received  with  one  another ;  and,  second,  the 
co-ordination  of  the  motions  expended  with  the  motions 
received,  and  with  one  another.    Hence  results  a  generalized 


THE  FUNCTIONS  OF  THE  NERVOUS  SYSTEM.        id 

idea  of  nervous  functions,  as  divisible  into  recipio-motor, 
liberu-motor,  and  dirigo-motor. 

It  must  be  admitted  tliat  in  tlieir  liiglier  forms,,  these 
functions  are  so  entangled  tliat  a  tripartite  division  of  them 
is  difficult,  if  not  impossible.  To  the  simplest  types  of 
nervous  structure,  the  classification  is  easily  applied :  each 
afierent  nerve  is  a  rccijjio-motor  agent ;  each  ganglion  is  a 
lihero-motor  agent;  each  afierent  nerve  is  a  dirigo-motor 
agent.  But  in  complex  nervous  systems,  formed  of  inferior 
and  superior  centres  connected  by  parts  containing  nerves 
that  are  centripetal,  centrifugal,  and  commissural,  there  arise 
corresponding  secondary  functions  which  greatly  obscure 
the  primary  functions.  It  remains  true  that  all  the  afi'erent 
nerves  are  receivers  of  motions,  and  that  all  the  efi'erent 
nerves  are  directors  of  motions ;  and  it  remains  true  that 
the  vesicles  and  portions  of  grey  substance  throughout  the 
centres  are  liberators  of  motions ;  but  of  the  fibres  largely 
composing  these  centres  we  must  say  that  their  functions 
are  both  receptive  and  directive.  Nevertheless,  we  shall 
be  considerably  helped  by  thinking  of  the  afi'erent  nerves 
as  recijjio-rnotor  and  the  efi'erent  nerves  as  dirigo-motor ; 
while  we  think  of  the  nervous  centres  as  composed  of 
lihero-motor  elements  along  with  elements  that  perform 
both  the  other  functions. 

This  general  conception  has  now  to  be  made  specific. 
In  dealing  with  functions  we  will  follow  the  same  order  as 
we  did  in  dealing  with  structures — we  will  consider  first  the 
offices  of  the  difi'erent  kinds  of  nervous  matter. 

§  19.  The  grey  substance  and  the  white  substance — or, 
to  speak  more  strictly,  the  nitrogenous  matter  in  and  around 
the  vesicles  and  the  nitrogenous  matter  occupying  the 
centres  of  the  nerve  tubes — have  not  absolutely  distinct 
duties.  Certain  simple  animals  yield  evidence  that  in  the 
rudimentary  nervous  system,  there  is  no  such  structural 
difi'erentiation  and  consequently  no  such  functional  diS'er- 
4 


50  THE    DATA   OF    PSYCHOLOGY. 

entiation;  and  there  is  proof  tliat  even  in  tlie  highest 
animals  the  diffcreutiation  is  incomplete. 

On  the  one  hand  the  vesicular  substance^  having  for  its 
chief  office  to  give  out  molecular  motion  when  disturbed_, 
has  also  a  considerable  power  of  conveying  or  conducting 
molecular  motion.  When  the  fibrous  parts  of  the  spinal 
cord  have  been  cut^  it  is  found  that  if  the  central  columns  of 
grey  matter  remain  uncut,  or  if  there  remains  even  a  naiTOAv 
link  to  maintain  the  continuity  of  the  grey  matter,  disturb- 
ance is  still  communicated  through  it  to  the  brain :  not,  in- 
deed, disturbance  of  any  special  kind,  but  disturbance  of  the 
most  general  kind.  True,  it  does  not  follow  that  such  dis- 
turbance passes  along  the  grey  matter  from  end  to  end. 
Throughout  the  whole  length  of  the  spinal  cord,  nerve-fibres 
divested  of  their  medullary  sheaths  enter  into  and  afterwards 
issue  from  the  grey  matter;  and,  again  protected  by  their 
sheaths,  proceed  upwards  to  the  brain  in  the  surrounding- 
white  matter.  Very  likely  these  take  up  and  convey  molecular 
disturbances  set  up  in  the  grey  matter  imbedding  them.  But 
even  this  implies  that  disturbances  are  propagated  to  some 
extent  through  the  grey  matter ;  and  the  argument  requires 
no  more. 

Conversely,  it  is  found  that  the  matter  forming  the  "  axis- 
cylinder,''  or  essential  nerve-thread,  can  do  something 
more  than  transmit  molecular  motion.  It  has  a  certain 
power  of  simultaneously  giving  out  molecular  motion : 
so  sharing  the  property  of  the  vesicular  matter.  When 
a  nerve  is  irritated  not  far  above  its  termination  in  a 
muscle,  the  efiect  is  but  small.  If  the  irritation  is  at  a  point 
further  removed  from  the  muscle,  the  efiect  is  greater.  And 
the  effect  increases  as  the  length  of  nerve  through  which  the 
disturbance  is  conveyed  increases.  From  this  we  must  infer 
that  besides  the  molecular  motion  received  and  transferred, 
there  is  molecular  motion  liberated  in  the  nerve-fibre  itself. 
Not  that  this  molecular  motion,  like  that  which  the  vesicular 
matter  yields  up,  implies  an  equivalent  decomposition.    Pro- 


THE    FUXCTIOXS   OP   THE    NERVOUS    SYSTEM.  51 

bably  it  is  a  concomitant  of  tlie  isomei'ic  transformation 
propagated  tlirougli  a  disturbed  nerve,  and  serving  to  con- 
vey tlie  disturbance.  Some  sucli  accompanying  result  is  to  be 
inferred,  a  irriori,  if  tbe  conduction  is  effected  by  isomeric 
transformation,  or  by  any  kind  of  molecular  re-arrangement. 
Wlien  the  molecules  of  a  mass  cliange  from  one  form  of 
combination  to  another,  either  absorption  or  liberation  of 
motion  is  sure  to  occur.  That  there  cannot  in  this  case 
be  absorption  of  motion  is  manifest;  since  that  would 
involve  a  proportionate  resistance  to  the  transfer — the  amount 
of  force  or  motion  received  by  the  extremity  of  the  nerve, 
would  quickly  be  used  up  in  transforming  the  adjacent  part 
of  the  nerve,  and  the  change  would  travel  but  a  little  way. 
Being  thus  obliged  to  infer  that  motion  is  liberated,  we  at 
once  see  whence  nerve-fibre  derives  the  power  to  increase 
the  disturbance  it  conveys  ;  since  each  portion,  while  passing 
on  the  wave  of  molecular  motion,  adds  the  molecular  motion 
given  out  during  its  own  transformation.  This  action  may 
be  rudely  symbolized  by  the  transfer  of  sensible  motion 
along  a  row  of  bricks  on  end,  so  placed  that  each  in  falling 
knocks  over  its  neighbour.  For  if  instead  of  bricks  which 
stand  on  tolerably  broad  ends  and  require  some  force  to 
overturn  them,  we  suppose  bricks  that  are  delicately 
balanced  on  narrow  ends ;  and  if  we  further  suppose  them 
so  constituted  that  they  do  not  dissipate  motion  by  per- 
cussion or  friction ;  we  shall  see  that  the  motion  transmitted 
will  accumulate.  Each  brick,  besides  the  motion  it  re- 
ceives, ^\'ill  pass  on  to  the  next  the  motion  which  it  has 
itself  gained  in  falling. 

The  general  truths  to  be  carried  with  us  are,  that  in  its 
primordial  undifferentiated  state,  nerve-matter  unites  the 
properties  of  giving  out  molecular  motion  and  convey- 
ing molecular  motion  ;  but  that  with  the  advance  of 
evolution,  it  becomes  specialized  into  two  kinds,  of  which 
the  one,  collected  together  in  masses,  has  mainly  the  function 
of  giving  out  motion,  though  it  can  still  to  some  extent  con- 


52  THE    DATA   OF    PSYCHOLOGY. 

duct  itj  wliilo  tlio  otlier,  collected  tog-otlier  in  threads^  has 
mainly  tlio  function  of  conducting  motioUj  tliougb.  it  can  still 
to  some  extent  give  it  out. 

§  20.  The  co-operation  of  these  differentiated  kinds  of 
nerve-substance,  having  difiereiitiated  functions,  is  seen  in 
its  simplest  form  where  they  aro  combined  into  what  was 
before  described  as  the  unit  of  composition  of  the  nervous 
system.  An  afferent  nerve,  changed  by  a  touch  at  its  outer 
end,  and  traversed  by  a  wave  of  isomeric  transformation  that 
gathers  strength  as  it  goes,  communicates  this  wave  to  the 
comparatively  large  mass  of  unstable  matter  connected  \ntli 
its  inner  end.  The  shock  of  molecular  disturbance,  im- 
mensely increased  by  the  decomposition  set  vip  in  this 
unstable  matter  constituting  a  ganglion-corpuscle  or  its 
matrix,  diffuses  itself  around,  but  takes  mainly  the  shape  of 
a  relatively-powerful  wave  of  isomeric  transformation  along 
the  efferent  nerve.  And  the  efferent  nerve  being  distributed 
at  its  other  end  among  the  fibres  of  a  muscle,  this  powerful 
wave  sets  up  in  them  an  isomeric  transformation  of  another 
kind,  resulting  in  contraction  {Princi^olcs  of  Biology,  §  303). 

The  belief  that  these  are  the  offices  of  the  respective  parts, 
is  borne  cut  by  those  peculiarities  of  structure  which  were 
described  as  occurring  in  the  afferent  fibres  of  certain 
special  sense-organs.  We  saw  that  the  outer  ends  of  the  optic 
nerve,  the  auditory  nerve,  and  the  olfactory  nerve,  are  alike 
characterized  by  the  presence  of  vesicular  matter ;  and  that 
Avhile  in  this  they  differ  from  the  outer  ends  of  the  nerves 
of  touch,  they  also  differ  in  being  excessively  sensitive.  If 
grey  matter,  or  the  matter  of  vesicles,  has  the  function  of 
immensely  multiplying  any  molecular  motion  it  receives,  and 
passing  on  the  augmented  wave  of  change  along  connected 
fibres,  we  at  once  have  a  satisfactory  explanation  of  these 
peculiar  peripheral  structures.  Take  as  an  example  the 
retina.  One  of  the  minute  cones  in  its  sensitive  layer, 
measuring  not  i^^oth  of  an  inch*  in  diameter,  has  its  com- 


THE  FUNCTIONS  OP  THE  NERVOUS  SYSTEM.        53 

ponenfc  matter  changed  by  tlie  etherial  vibrations  emanating 
from  a  candle  in  a  cottage-window  at  a  great  distance.  The 
infinitesimal  impact  received  from  so  faint  a  ray,  may  well  bo 
supposed  insufficient  to  send  through  a  considerable  length 
of  afferent  nerve,  an  adequately-rapid  wave  of  molecular 
change ;  but  this  wave,  after  passing  through  an  extremely 
delicate  fibril  less  than  ^  of  an  inch  in  length,  comes  to  a 
layer  of  ganglion-corpuscles,  with  one  of  which  we  may 
presume  that  it  unites.  In  this  the  minute  disturbance  sets 
up  destructive  molecular  change — unlocks  a  considerable 
amount  of  molecular  motion ;  and  thus  greatly  augmented, 
the  wave  of  transformation  traverses  the  remainder  of  the 
afferent  nerve  without  that  loss  of  time  that  would  result 
had  it  to  gain  strength  by  a  series  of  increments,  starting 
from  an  infinitesimal  first  term. 

How  such  appliances  for  multiplying  action  co-operate 
in  these  cases  where  the  initial  action  is  excessively 
minute,  may  be  illustrated  by  certain  artificial  appli- 
ances that  co-operate  in  an  analogous  manner.  A  man 
with  a  hair-trigger  pistol  in  his  hand,  puts  its  muzzle  to 
the  end  of  a  train  that  rans  to  a  powder-magazine.  The 
slightest  pressure  on  the  trigger  liberates  a  spring,  and 
this  drives  down  the  hammer.  Here  is  something  like  the 
external  multiplier  which,  as  Ave  have  seen,  habitually 
intensifies  the  action  that  falls  on  the  end  of  an  afierent 
nerve.  The  propelled  hammer  explodes  the  unstable 
detonating  powder  in  the  cap ;  thus  playing  a  part  com- 
parable to  that  of  the  concentrated  pencil  of  light,  which 
causes  decomposition  in  one  of  the  minute  sensitive  rods  or 
cones  of  the  retina.  The -explosion  of  the  cap  explodes  the 
powder  in  the  pistol :  a  change  that  may  symbolize  the 
setting  up  of  decomposition  in  an  adjacent  ganglion-cell  by 
a  disturbed  retinal  element.  The  flash  from  the  mouth  of 
the  pistol  fires  the  train,  which,  carrying  the  flame  onwards, 
blows  up  the  magazine;  and  this  serves  to  illustrate  the 
action  of  the  partially-decomposed  ganglion-cell  which  pro- 


54  THE    DATA   OP   PSYCHOLOGY. 

pngatcs  a  sliock  tlirough  tlie  afferent  nerve  to  a  large  de- 
posit of  unstable  matter  in  tlie  optic  centre,  wliere  an  immense 
amount  of  molecular  motion  is  thereupon  disengaged. 

The  joint  action  of  an  afferent  fibre,  its  centrally-seated 
ganglion-  corpuscle,  and  the  connected  efferent  fibre,  is  com- 
monly known  as  a  reflex  action.  The  name  indicates  the 
general  truth  that  the  disturbance  in  travelling  from  its  place 
of  origin  to  the  place  where  its  effect  is  seen,  passes'  through 
a  point  at  which  its  course  is  bent  or  reflected ;  and  in  so  far 
as  it  describes  this  very  general  trait  the  term  is  a  good 
one.  But  if  the  foregoing  interpretation  be  correct,  the 
term  is  in  other  respects  objectionable.  On  the  one  hand,  it 
implies  as  essential  what  is  non-essential.  That  the  wave 
of  disturbance  makes  a  sudden  tvirn  at  one  part  of  its 
course,  is  a  fact  of  no  intrinsic  moment — is  merely  a  con- 
comitant of  the  fact  that  the  nerves  it  traverses  have  to  be 
put  in  communication  with  other  nerves,  and  that  points  of 
junction  imj^ly  angles.  On  the  other  hand,  it  leaves 
out  of  sight  the  fact  that  one  of  these  points  of  junction 
from  which  the  wave  of  disturbance  is  said  to  be  reflected, 
is  a  place  at  which  it  is  greatly  augmented ;  and  that  this 
augmentation  of  the  wave  is  the  all-important  office  of  the 
matter  lying  at  the  point  of  junction. 

§  21.  Remembering  that  bundles  of  such  afferent  nerves 
are  joined  to  bundles  of  such  efferent  nerves,  by  clusters  of 
such  corpuscles  imbedded  in  the  grey  matter  of  a  ganglion, 
and  that  bundles  of  centripetal  nerves  proceed  thence  to 
hifj-hcr  ganglia;  we  have  next  to  consider  the  functions  of 
these  structures  as  wholes. 

A  nervous  centre,  even  of  an  inferior  order,  is  not  simj)ly 
a  place  where  afferent  nerves  are  severally  linked  with  their 
corresponding  efferent  nerves,  by  corpuscles  or  portions  of 
grey  matter  that  multiply  and  pass  on  disturbances;  nor 
is  the  only  further  office  it  serves  that  of  sending  to  higher 
ganglia,  portions  of  these  disturbances ;  but   it  is  also  a 


THE    FUXCTIOXS    OP   THE    NERVOUS    SYSTEM.  55 

place  wliere  more  inyolved  communications  arc  cfiectcd. 
For  in  all  ganglia  save,  perhaps,  tlie  very  simplest, 
the  corpuscles  or  vesicles  give  off  processes  more  or  less 
numerous,  and  usually  more  or  less  branched ;  and  these 
branched  processes,  spreading  through  the  matrix  of  grey 
matter,  may  be  assumed  to  propagate  in  various  directions, 
and  various  degrees,  the  disturbance  set  up  in  the  corjauscle. 
This  diffusion  of  liberated  molecular  motion  has  two  im- 
plications. First,  the  number  and  complexity  of  the  cor- 
related changes  produced  by  the  original  change,  increase 
with  the  multiplication  and  variety  of  these  processes  and 
their  connexions.  And,  second,  along  with  increase  in  the 
number  of  correlated  changes,  there  goes  increase  in  the 
total  quantity  of  molecular  motion  given  out,  directly  or 
indirectly. 

Fully  to  understand  the  importance  of  this  last  implica- 
tion, it  is  needful  to  refer  back  to  Fig.  4,  and  to  the  accom- 
panpng  description  of  the  way  in  which  a  nervous  centre 
that  serves  to  establish  the  various  possible  relations  among 
different  points  in  an  organism,  must  contain  a  large  accu- 
mulation of  these  connecting  and  multiplying  links;  and 
where  it  was  shown  how  immense  must  become  the  accumu- 
lation of  vesicular  matter  in  a  centre  that  has  the  ofl&ce  of 
establishing  relations  among  these  many  parts  in  various 
orders.  For  it  will  be  seen  that  as  fast  as  the  connexions 
become  numerous  and  complex,  so  fast  will  enlarge  the 
crowds  of  these  connecting  corpuscles  and  multipliers  of 
disturbance  which  simultaneously  come  into  action.  And 
hence  the  quantity  of  molecular  motion  evolved  in  tlie 
nervous  centres  will  become  great  in  proportion  as  the 
nervous  relations  increase  in  integration  and  heterogeneity. 

When  we  see  how  the  arrangements  for  liberating  and 
multiplying  motion,  described  under  their  simple  form  in 
the  last  section,  are  thus  compounded — when,  recmTing 
to  our  simile,  we  see  how  the  first  central  magazine  of  force 
exploded,  communicates  with  other  larger  magazines,  and 


60  THE    DATA   OF   PSYCHOLOGY. 

tliese  again  witli  still  larger,  wliicli  are  subsequently  ex- 
ploded; we  sliall  be  at  no  loss  to  understand  liow  tbe 
sliglitest  impression  on  one  of  tbe  recijpio-motor  nerves, 
may  evoke  from  the  Uhero-motor  centres  a  relatively-in- 
commensurable amount  of  force,  wliicli,  discharged  along 
the  dir'ujo-motor  nerves,  may  generate  violent  muscular 
contractions.  So  that,  to  take  a  case,  a  slight  sound  may 
produce  a  convulsive  start  of  the  whole  body;  or  an  un- 
expected motion  of  some  adjacent  object,  infinitesimal  as  is 
the  modification  it  produces  in  the  retina,  may  neverthe- 
less cause  an  involuntary  jump  and  scream. 

§  22.  In  treating  nervous  functions  in  general,  I  have 
unawares  ended  with  illustrations  from  the  nervous  func- 
tions of  human  beings :  so  coming  to  the  division  of  the 
subject  on  which  we  have  next  to  enter.  For  the  brief 
account  given  in  the  last  chapter  of  the  special  nervous 
sti'uctures  with  which  we  are  most  concerned,  must  here  be 
supplemented  by  a  brief  account  of  their  special  functions. 

If  we  leave  out  such  afierent  and  efierent  fibres  as  pass 
through  the  spinal  cord  to  and  from  the  encephalon,  and  also 
those  centripetal  and  centrifugal  fibres  which  connect  its 
various  parts  with  the  encephalon,  we  may  regard  the  partly 
dependent  and  partly  independent  centres  composing  the 
spinal  cord,  as  being  co-ordinators  of  the  actions  performed 
by  the  skin  and  muscles  of  the  trunk  and  limbs.  A  large 
proportion  of  these  actions,  including  many  of  considerable 
complexity,  the  sjoinal  cord  is  able  to  co-ordinate  without 
aid  from  the  higher  centres;  and  some  of  the  partially- 
differentiated  centres  composing  the  spinal  cord,  are  able  to 
effect  simple  co-ordinations  without  aid  from  the  rest.  Wc 
will  glance  at  these  simple  co-ordinations  first.  If 

a  patient  paralyzed  by  some  injury  of  the  spinal  cord  that 
has  left  the  lumbar  enlargement  intact,  has  his  foot  touched, 
the  leg  is  quickly  withdrawn ;  not  only  without  a  cerebral 
act,  but  even  without  his  brain  being  in  any  way  affected. 


THE   rimCTIONS    OP   THE    NERVOUS    SYSTEM.  57 

unless  indirectly  by  the  shaking  of  tlie  bed.  Tlius  the 
branched  corpuscles  and  fibres  contained  at  that  point  in 
the  cord  with  which  the  afferent  and  efferent  nerves  of 
the  leg  are  connected,  have  at  once  the  function  of  giving 
out,  when  the  disturbance  is  communicated  to  them,  the 
requisite  quantity  of  molecular  motion,  and  of  so  directing 
this  to  the  respective  muscles  of  the  leg,  as  to  cause  the 
appropriate  movement.  More  involved  co-ordi- 

nations are  effected  by  the  co-operation  of  several  such 
centres,  or  portions  of  the  grey  substance,  contained  in 
adjacent  parts  of  the  spinal  cord.  In  the  human  subject 
demonstration  of  this  is  not  easy ;  but  it  is  shown  by  ex- 
periments on  inferior  Vertehrata.  A  decapitated  frog  that 
has  its  side  irritated,  will  bring  the  hind  foot  of  that  side 
to  the  spot,  and  move  it  so  as  to  displace  the  irritating 
object.  Even  something  further  is  done.  If  a  scalpel  be 
applied  to  the  skin  between  the  hind  legs,  these  act  jointly 
in  such  a  manner  as  to  push  away  the  scalpel.  The  explana- 
tion is  that  by  commissural  fibres,  transverse  and  longi- 
tudinal, the  disturbances  conveyed  to  particular  centres, 
are  communicated  to  sundry  adjacent  centres ;  and 
through  their  efferent  nei'ves  these  direct  and  appor- 
tion the  multiplied  disturbances  among  a  great  variety 
of  muscles.  How  such  definite  co-ordinations 

as  these  are  effected  by  such  an  apparatus,  we  shall  better 
understand  on  remembering  that  the  relations  between 
positions  on  the  skin  and  the  movements  needed  to  bring 
the  extremities  to  touch  them,  are  tolerably  constant.  A 
frog's  hind  foot  can  reach  a  given  point  on  the  frog's  side, 
only  by  one  particular  muscular  adjustment ;  or,  at  any  rate, 
by  a  muscular  adjustment  that  varies  within  narrow  limits. 
And  since  in  all  frogs,  generation  after  generation,  the  pro- 
portions of  parts,  and  therefore  the  relations  of  muscular 
adjustments  to  given  positions,  remain  practically  the  same ; 
it  becomes  comprehensible  how,  through  the  organized 
nervous  connections  that  arise,   a  touch  at  any  point  may 


58  'the  data  of  psychology. 

cause  tlie  combined  contractions  needful  to  bring  tlie  end 
of  the  limb  to  that  point.  It  should  be  observed 

here,  that  the  conception  of  these  acts  of  the  spinal  cord  as 
co-ordinations  of  motions,  is  incomplete  so  long  as  the  only 
motions  contemplated  are  those  of  the  muscles.  Under  the 
head  of  motions  must  be  included  the  disturbances  con- 
veyed along  the  afferent  nerves  ;  for  the  muscular  motions 
are  so  adjusted  that  their  joint  results  have  special  rela- 
tions to  these  received  disturbances.  The  co-ordination 
is  between  the  recipio-motor  acts  and  the  clirigo-motor 
acts.  We  may,  then,  regard  the  spinal  cord  as  a 

centre  of  co-ordinations  which,  though  some  of  them  have 
considerable  complexity,  are  yet  relatively  simple — simple, 
inasmuch  as  the  disturbances  received  from  the  skin  are 
much  alike  from  all  parts ;  simple,  inasmuch  as  each 
muscular  adjustment  is  mainly  of  a  fixed  or  invariable  kind; 
and  simple,  inasmuch  as  the  component  acts  of  the  co- 
ordinated group  are  practically  simultaneous. 

That  enlarged  and  differentiated  part  of  the  spinal  cord 
called  the  medulla  oblongata,  including  the  root-portion  of 
the  j:)o;is  Varolii,  adnate  with  it  and  structurally  so 
entangled  that  the  two  cannot  be  demarcated,  we  may 
roughly  distinguish  as  a  centre  of  compound  co-ordination. 
It  receives  directly  the  auditory  impressions,  the  impressions 
of  taste,  and,  indirectly  through  the  corpora  quaclrigemina,  is 
affected  by  visual  impressions  :  meanwhile  sending  impulses 
to  the  various  muscles  of  the  eyes,  the  face,  the  jaws,  and 
the  mouth.  By  it  the  movements  of  all  four  limbs  are  com- 
bined in  joint  acts ;  and  by  simultaneously  regulating  them, 
it  makes  the  head  and  jaws  co-operate  with  the  limbs.  The 
various  impressions  and  muscular  motions  implied  by  the 
act  of  swallowing,  it  brings  into  due  relation.  Eeceiving 
the  respiratory  stimulus,  it  emits  the  stimuli  to  those 
muscles  which  enlarge  and  diminish  the  thoracic  cavity,  so 
causing  inspiration  and  expiration ;  and,  as  a  consequence,  it 
is  the  centre  which,  disturbed  by  the  more  violent  irritations 


THE   FUNCTIONS   OP   THE   NERVOUS    SYSTEM.  59 

of  the  respiratory  surface,  sends  out  to  tlie  respiratory 
muscles  tliose  more  violent  impulses  whicli  cause  coughing 
and  sneezing :  to  whicli  may  be  added,  as  actions  belonging 
to  tlie  same  class,  crying  and  yawning.  Lastly,  through 
the  pneumogastric  nerve,  it  controls  the  action  of  the  heart, 
and  the  actions  of  other  viscera.  Thus  it  is  a  centre  to 
which  come,  in  some  cases  directly  but  in  most  cases  in- 
directly, impressions  from  all  parts  of  the  external  surface, 
as  well  as  from  the  mucous  lining  of  the  mouth, 
oesophagus,  and  lungs ;  and  to  which  there  also  come, 
directly  or  indirectly,  impressions  received  through  the 
higher  senses.  At  the  same  time  the  minor  centres  severally 
commanding  groups  of  muscles,  are  by  it  put  in  relation 
with  one  another;  and  their  respective  simple  actions  so 
combined  as  to  constitute  compound  actions.  In  short  it 
has  reeipio-motor  relations  with  all  the  parts  that  hold  con- 
verse with  the  external  world,  while  it  has  dirigo-motor 
relations  with  all  the  parts  that  react  on  the  external  world; 
and  its  function  is  that  of  adjusting  the  complex  movements 
in  obedience  to  the  complex  stimuli.  This  is  not  all.  Being 
the  centre  which  initiates  and  directs  involved  and  extensive 
bodily  actions,  entailing  rapid  expenditure,  it  is  the  centre 
in  which  the  demand  for  materials  is  indicated ;  and  hence  it 
becomes  the  regulator  of  the  circulation,  of  the  aeration  of  the 
blood,  and  of  the  visceral  actions  generally.  Clearly,  then, 
its  co-ordinations  are  compound  in  comparison  with  those  of 
the  spinal  cord — compound,  because  the  impressions  which 
afferent  and  centripetal  nerves  bring  to  it,  are  not  only  more 
numerous  but  also  more  heterogeneous ;  compound,  because 
the  impulses  which  it  sends  out  are  also  more  numerous  and 
more  heterogeneous ;  and  compound,  because  it  brings  more 
involved  acts  into  correspondence  with  more  involved  stimuli. 
The  functions  of  the  two  still  higher  centres,  the  cere- 
helium  and  the  cerebrum,  have  now  to  be  defined  in  terms 
of  the  same  nature.  How  shall  we  express  them  ?  Both 
of  these  great  bi-lobed  masses  arise  as  buds  out  of  tho 


60  THE    DATA   OP   PSYCHOLOGY. 

originally  almost-uniform  cranio-spinal  axis ;  and  as  tlicy 
enlarge^  tlicir  distal  portions  grow  more  massive  than  tlioir 
proximal  portions,,  so  tliat  tlicy  end  in  being  pedunculated. 
Eacli  of  them  tlius. bears  to  the  medulla  oblongata,  a  relation 
like  tliat  wliicli  tlie  superior  ganglion  H,  in  the  diagrammatic 
Fig.  4,  bears  to  the  inferior  ganglion  F  ;  and  we  may  not 
unreasonably  infer  that  their  functions  are  analogous  to 
those  hypothetically  assigned  to  the  ganglion  H.  That  is  to 
say,  we  may  regard  them  as  organs  of  doubly-compound  co- 
ordination— organs  which  have  for  their  common  function, 
the  re-combining  into  larger  groups,  and  into  countless 
different  orders,  the  already-complex  impressions  received 
by  the  medulla  ohlongata;  and  which  have  the  further 
function  of  so  arranging  the  already-complex  motor  im- 
pulses issuing  from  the  medulla  ohlongata,  as  to  form  those 
far  more  involved  aggregate  actions,  simultaneous  and 
successive,  which,  being  adjusted  to  these  involved  im- 
pressions, achieve  remote  ends.  The  general  truth  of  this 
definition  may,  I  think,  be  safely  assumed;  since  it  is 
simply  a  statement  in  other  terms,  of  what,  in  ordinary 
language,  is  called  intelligent  action;  which  habitually 
characterizes  vertebrate  animals  in  proportion  as  these 
centres  are  largely  developed.  Thus  much  being  granted, 
there  arises  the  further  question — what  are  the  respective 
parts  played  by  these  two  great  organs  in  this  doubly-com- 
pound co-ordination  ?  Much  difference  of  opinion  has  long- 
existed,  and  still  exists,  respecting  the  particular  offices  of 
these  supreme  ganglia ;  and  especially  respecting  the  office 
of  the  cerebellum.  Without  committing  myself  to  it  as 
anything  more  than  a  hypothesis,  I  will  here  venture  to 
suggest    a    not   improbable    interpretation.  The 

common  function  of  the  two  being  that  of  co-ordinating  in 
larger  groups  and  in  various  orders,  the  impressions  and 
acts  co-ordinated  in  the  lower  centres,  we  may  fitly  ask — ■ 
are  there  any  fundamentally  distinct  kinds  of  order  in  which 
impressions  and  acts  may  be  co-ordinated  ?     The  obvious 


THE   FUNCTIONS    OP   THE   NEKVOUS    SYSTEJI.  Gl 

answer  is,  that  there  are  the  two  fundamentallj  distinct 
orders  of  Co-existence  and  Sequence.  All  phenomena  are 
presented  to  ns  either  as  existing  simultaneously  or  as 
existing  succcssivel}^  If,  then,  these  two  highest  nervous 
centres,  which  together  perform  the  general  function  of 
doublj-compound  co-ordination,  take  separate  parts  of  this 
function,  as,  from  their  separateness,  we  must  conclude  that 
they  do ;  we  can  scarcely  make  a  more  reasonable  assump- 
tion than  that  the  respective  orders  in  which  they  co- 
ordinate compound  impressions  and  acts,  answer  to  the  re- 
spective orders  in  which  phenomena  are  conditioned.  In 
brief,  the  hypothesis  thus  reached  a  priori,  is  that  the 
cerebellum  is  an  organ  of  doubly-compound  co-ordination 
in  space;  while  the  cerebrum  is  an  organ  of  doubly-com- 
pound co-ordination  in  time.  The  a  posteriori 
evidence,  so  far  as  I  have  examined  it,  appears  congruous_, 
both  with  this  view  of  the  general  function  of  these  centres, 
and  with  this  view  of  their  respective  special  functions. 
There  is  complete  harmony  between  the  hypothesis  and  the 
seemingly-strange  facts  that  these  centres  may  be  partially 
destroyed  without  causing  obvious  incapacity,  and  that 
they  may  be  wholly  removed  without  destroying  the  ability 
to  co-ordinate  the  less  complex  impressions  and  acts.  As- 
suming, as  Ave  may  fairly  do,  that  the  cells  and  fibres  which 
subserve  the  more  involved  co-ordinations,  are  successively 
added  at  the  surfaces  of  these  centres  as  they  develop,  it  is 
inferable  that  the  superficial  parts  may  be  sliced  off  with, 
the  least-appreciable  effects  on  the  actions;  and  that  the 
effects  on  the  actions  will  become  conspicuous  in  proportion 
as  the  slices  destroy  the  parts  nearer  to  the  lower  centres : 
and  these  are  the  results  established  by  experiment.  Besides 
finding,  as  the  hypothesis  leads  us  to  expect,  that  these 
nervous  masses  are  relatively  large  in  all  creatures  capable 
of  adjusting  their  involved  and  continuous  actions  to 
complex  and  distant  environing  agencies ;  we  also  tracG 
some   relation   between   the  development  of  each  and  tlio 


62  THE   DATA   OP   PSYCHOLOGY. 

peculiar  capacities  of  the  species.  There  is,  for  instance, 
the  fact  that  the  cerebellum  is  unusually  developed  in  birds 
of  prey,  which  have  to  co-ordinate  with  great  accuracy  the 
relations  of  distance,  direction,  and  complex  form,  as  well  as 
very  precisely  to  co-ordinate  the  involved  movements  ap- 
propriate to  these  involved  impressions.  And  there  is,  on 
the  other  hand,  the  fact  that  the  cerebrum  predominates  in 
creatures  showing,  like  ourselves,  the  power  of  adapiing, 
throughout  long  periods,  concatenated  compound  actions  to 
concatenated  compound  impressions.* 

Of  course  this  classification  of  the  functions  of  the  nervous 
centres,  as  co-ordinations  that  are  simple,  compound,  and 
doubly  compound,  must  be  taken  as  merely  approximate. 
No  definite  divisions  can  be  made.  The  functions  arise 
through  increasing  complications;  and  these  general  con- 
trasts become  conspicuous  only  when  we  look  at  the 
facts   in  their  main   outlines.     Here,    however,    where   the 

*  Let  me  here  draw  attention  to  papers  in  the  Medical  Times  and  Gazette, 
for  December  14  and  December  21,  1867,  in  which  Dr.  Hughlings  Jackson  has 
published  some  facts  and  inferences  that  quite  harmonize  with  these  interpre- 
tations, in  so  far  as  the  common  fiiuction  of  the  great  nervous  centres  is 
concerned. 

It  should  be  remarked  that  the  above-proposed  definitions,  are,  to  a  con- 
siderable extent,  coincident  with  current  conceptions.  The  cenhriim  is 
generally  recognized  as  the  chief  organ  of  mind  ;  and  mind,  in  its  ordinary 
acceptation,  means  more  especially  a  comparatively  intricate  co-ordination  in 
time — the  consciousness  of  a  creature  "looking  before  and  after,"  and  using 
past  experiences  to  regulate  future  conduct.  In  like  manner  the  function 
ascribed  to  the  cerebellum  in  the  foregoing  paragraph,  partially  agrees  with 
that  which  M.  Flourens  inferred  from  his  experiments.  It  differs,  however,  in 
two  respects.  It  implies  that  the  cerebellum  is  not  an  organ  for  the  co-ordi- 
nation of  motions  only,  or  of  synchronous  motions  only ;  but  that  it  is  also  an 
organ  for  the  co-ordination  of  simultaneous  impressions,  and  for  tlie  co-ordi- 
nation of  the  synchronous  motions  in  adaptation  to  the  simultaneous  impres- 
sions. And  it  further  implies  that  not  all  simultaneous  imin-essioiis  and 
adapted  synchronous  motions  are  co-ordinated  by  the  cerebellum  ;  but  only  the 
doubly-compound  ones,  which  have  for  their  external  correlatives  the  intricate 
combinations  of  attributes  that  distinguish  objects  from  one  another,  and  the 
more  multiplied  and  varied  localizations  of  objects  in  the  space  that  extends 
beyond  the  immediate  limits  and  reach  of  the  organism. 


THE  FUNCTIONS  OF  THE  NERVOUS  SYSTEM.        63 

object  is  to  give  an  idea  of  tlie  principles  of  nervous  func- 
tion in  its  successive  stages  of  evolution,  detailed  qualifica- 
tions do  not  concern  us. 

§  23.  A  few  words  are  due  to  tlie  functions  of  that  sub- 
ordinate nervous  apparatus,  the  structure  of  which  we 
glanced  at  in  the  last  chapter — the  nervous  apparatus  pre- 
siding over  the  vital  processes.  It  will  suffice  if  we  take 
the  functions  of  the  vaso-motor  di^asion  of  it  as  exemplifying 
the  whole. 

Each  vaso-motor  nerve,  having  roots  in  both  the  cerebro- 
spinal system  and  the  sympathetic  system,  conveys  to  all 
branches  of  the  artery  it  accompanies,  the  impulses  arising 
from  the  activities  of  the  great  nervous  centres  and  muscles, 
as  well  as  from  the  activities  of  the  viscera.  Probably  the 
ordinary  amount  of  disturbance  propagated  along  each  vaso- 
motor nerve,  simply  excites  the  muscular  coats  of  the  adja- 
cent artery  sufficiently  to  maintain  its  due  elasticity.  But 
stronger  disturbances  produce  marked  alterations  of  its 
calibre :  those  brought  by  the  sympathetic  fibres  being- 
said  to  cause  contraction ;  and  those  brought  by  fibres  from 
the  cerebro-spinal  system  being  said  to  cause  dilatation. 
Some  of  these  changes  have  relation  to  actions  going  on 
in  the  part  itself;  and  others  to  actions  going  on  in  the 
chief  vital  organs,  or  in  the  body  as  a  whole.  But  all 
of  them  show  us  that  by  means  of  the  vaso-motor  nervous 
system,  the  blood-vessels  are  so  regulated  as  to  subserve 
general  and  local  needs.  One  further  fact  beloug- 

ing  to  this  class  may  be  added ;  partly  because  of  its  in- 
trinsic interest,  and  partly  because  it  illustrates  certain 
supplementary  nervous  functions  not  hitherto  named.  We 
have  already  seen  that,  among  its  many  duties,  the 
medulla  oblongata  controls,  through  the  medium  of  the 
pneumogastric  nerve,  the  action  of  the  heart.  So  long 
as  the  disturbance  conveyed  to  the  medulla  oblongata,  either 
from  the  periphery  of  the  nervous  system  or  from  its  great 


64  THE    DATA   OP    PSYCHOLOGY. 

centres^  does  not  exceed  a  moderate  amount,  the  resulting 
waves  of  molecular  cliangc  sent  by  it  throug-li  tlio  pneumo- 
gastric,  do  not  interfere  with  the  heart's  action — perhaps  en- 
force it.  But  when  the  medulla  is  excessively  disturbed,  the 
increased  quantity  of  stimulus  it  sends,  either  diminishes  the 
action  of  the  heart,  or  stops  it  altogether:  so  causing  arrest 
of  the  circulation  and  consequent  insensibility.  Noting,  as 
we  pass,  that  this  is  one  of  the  most  remarkable  forms  of 
that  co-ordination  which  the  nervous  system  everywhere 
effects,  since  the  arrangement  is  such  that  when  the  nervous 
system  becomes  abnormally  active,  and  its  chief  centres  sur- 
charged with  blood,  they  themselves  arrest  the  organ  which 
propels  blood  to  them ;  we  have  to  ask  how  it  happens  that 
in  this  case  the  propagation  of  disturbance  through  a  nerve 
checks  action  instead  of  causing  it.  The  reply  is  that  in 
addition  to  the  systems  of  nerves  which  excite  action,  there 
is  found  to  exist  a  system  of  nerves  which  diminish  action — 
inJiihifory  nerves  as  they  are  called.,  Through  these  it  is 
alleged  that  the  brain  controls  the  spinal  cord — restraining 
those  reflex  movements  which^  when  connection  with  the 
brain  is  cut  off,  become  so  much  more  marked.  And  through 
one  of  these  it  is  concluded  that  the  medulla  ohlongata  reins 
in  the  heart,  when  the  cerebral  irritation  is  excessive. 

Bo  this  as  it  may,  the  facts  named  illustrate  the  way  in 
which  the  nervous  system,  Avhile  it  co-ordinates  the  external 
actions,  also  co-ordinates  those  internal  actions  which  make 
them  possible.  The  reader  has  but  to  conceive  that  through 
other  systems  of  nerves,  other  organs  which  absorb,  secrete, 
excrete,  &c.,  are  similarly  controlled,  and  he  will  under- 
stand sufficiently  for  present  purposes,  how  demand  for 
materials  and  supply  of  materials  are  harmonized. 

§  21<.  In  summing  up  the  functions  of  the  nervous  s3-stem 
as  thus  formulated  in  terms  of  motion,  it  will  be  useful  to 
observe  the  greater  comprehensiveness  of  view  we  obtain 
by  excluding  the  ordinary  implications. 


THE  FUNCTIONS  OP  THE  NERVOUS  SYSTEM,        65 

When  one  pai*t  of  a  Zoopliyte  is  touched^  tlie  contraction 
set  up  in  that  part  slowly  diffuses  itself  through  the  whole 
body.  Two  things  are  here  to  he  noted.  There  is  a  propa- 
gation of  disturbance  through  the  nerveless  sarcodc  of 
which  the  creature  is  composed ;  for  distant  parts  are 
eventually  affected.  There  is  also  an  increase  of  disturb- 
ance ;  for  in  successive  moments  the  mass  of  tissue  under- 
going change  is  greater.  Thus  the  relatively-homogeneous 
substance  of  these  simple  animals,  exhibits  the  two  essential 
phenomena  exhibited  by  the  nervous  system  in  all  phases  of 
its  development :  there  is  propagation  of  molecular  motion, 
and  there  is  a  simultaneous  augmentation  of  this  mole- 
cular motion.  Such  essential  phenomena  grow  more  con- 
spicuous as  the  nervous  system  develops,  partly  because  the 
changes  set  up  become  limited  to  narrow  lines  and  small 
masses,  and  partly  because  the  matter  of  which  these  are 
formed  becomes  distinguished  by  an  increased  degree  of 
the  general  instability.  Since,  then,  the  functions  of  the 
nervous  system  as  expressed  in  terms  of  molecular  motion, 
are  functions  exhibited  in  a  vague  way  by  the  undifferentiated 
tissue  from  which  the  nervous  system  insensibly  arises  ;  it  is 
clear  that  by  so  expressing  them  we  include  alike  their 
lowest  and  their  highest  forms,  which  we  cannot  otherwise 
do. 

Moreover,  only  in  these  terms  can  there  be  given  an 
adequate  definition  of  fully  -  developed  nervous  functions. 
If  we  admit  any  subjective  element,  our  definition  becomes 
inapplicable  to  all  those  nervous  actions  which  have  no  sub- 
jective accompaniments — which  go  on  without  feelings ; 
and  a  conception  of  nervous  functions  which  excludes  those 
of  organic  life,  cannot  be  a  complete  concej^tion.  On  the 
other  hand,  the  definition  of  nervous  functions  as  consist- 
ing in  the  conveyance  and  multiplication  of  molecular 
motions,  holds  in  all  cases.  It  includes  equally  the  conduc- 
tion of  an  impression  made  on  a  nerve  of  sense,  and  the 
excitement  of  chemical  metamorphoses  in  a  gland. 


66  THE    DATA   OF    PSYCHOLOGY. 

Tlie  subdivision  of  tliis  general  function  under  tlie  above- 
proposed  licads  of  recipio-motor,  lihcro-motor,  and  dirigo- 
motor,  lias  also  tlie  advantage  of  greater  compreliensive- 
ness.  No  word  at  present  in  use  expresses  the  office  whicli 
afferent  nerves  liave  in  common,  more  specifically  than  the 
word  afferent  itself  expresses  it.  Whether  disturbance  of 
its  outer  end  produces  in  an  afferent  nerve  a  change  causing 
a  reflex  contraction,  or  whether  it  produces  a  change  causing 
what  we  call  a  sensation,  is  a  circumstance  of  secondary 
import ;  as  is  proved  by  the  fact  that  by  use  the  last  may 
become  the  first.  The  essential  thing  common  to  the  two, 
is  that  molecular  motion  is  propagated  from  periphery  to 
centre.  So,  too,  is  it  with  the  libero-mofor  functions. 
Whether,  as  in  the  ganglia  of  the  sympathetic,  the  multipli- 
cation of  communicated  disturbance  has  no  subjective  con- 
comitant, or  whether,  as  in  the  cerehrum,  it  has  a  subjective 
concomitant,  there  is  in  both  cases  a  liberation  of  molecular 
motion;  and  this,  being  the  common  character  of  the 
changes  in  nerve-centres,  must  determine  the  definition  of 
their  common  function.  In  like  manner,  all  efierent  nerves, 
whether  conveying  disturbances  that  set  up  contractions  in 
muscles,  or  cause  constrictions  of  arteries,  or  excite  chemical 
transformations  in  glands,  serve  to  direct  the  waves  of 
molecular  motion — waves  that  are  intrinsically  alike  in 
nature,  though  the  results  produced  by  them  in  the  organs 
to  which  they  are  carried  differ  so  widely,  and  though  they 
are  now  associated  with  consciousness  and  now  are  not. 

A  more  special  view  of  the  functions  thus  classed,  dis- 
closes two  essential  facts.  Considered  as  an  agent  for 
generating  movements,  we  see  that  the  nervous  system  acts 
by  liberation  of  successively-larger  amounts  of  molecular 
motion  in  the  centres  successively  disturbed.  A  very  small 
change  at  the  outer  end  of  an  afferent  nerve,  sets  up  a 
relatively-large  quantity  of  change  in  some  adjacent  un- 
stable nerve-matter ;  whence  the  change,  thus  increased,  is 
propagated  to  some  internal  ganglion ;  to  be  passed  on  by 


THE    FUNCTIONS    OF    THE    NERVOUS    SYSTEM.  67 

ifc  immensely  multiplied  as  before ;  until  tliere  is  unlocked 
an  amount  of  disturbance  capable  of  causing  muscular  con- 
tractions tbrougbout  the  whole  body. 

Meanwhile  these  centres  in  which  molecular  motion  is 
liberated,  are  also  'the  centres  in  which  it  is  co-ordinated ; 
and  the  successively  higher  and  larger  centres  which  evolve 
successively  larger  quantities  of  molecular  motion,  are  also 
centres  in  which  successively  more  complex  co-ordinations 
are  effected.  Whence  follows  the  general  result  that  along 
with  each  further  development  of  the  nervous  system, 
enabling  it  to  make  all  parts  of  the  body  work  together 
more  efficiently  in  simultaneous  and  successive  actions, 
there  goes  an  increased  power  of  evolving  the  energy  re- 
quired for  such  larger  aggregates  of  actions. 

These  principles  we  found  to  be  well  exemplified  in  the 
case  which  most  nearly  concerns  us.  It  is  needless  to 
I'e-state  the  results  so  recently  arrived  at.  One  remark, 
however,  may  be  added.  In  the  functions  of  the  suc- 
cessively-higher vertebrate  centres,  reaching  their  climax 
in  the  human  being,  we  see  well  exemplified  the  law  of 
development  of  functions  in  general  (First  Princii^les, 
Part  II.  §  142).  This  progress  from  co-ordinations  that 
are  small  and  simple  to  those  that  are  larger  and  compound, 
and  to  those  that  are  still  larger  and  doubly  compound,  is 
one  of  the  best  instances  of  that  progressive  integration  of 
motions,  simultaneously  becoming  more  heterogeneous  and 
more  definite,  which  characterizes  Evolution  under  all  its 
forms. 


CHAPTER  lY. 

THE    CONDITIONS    ESSENTIAL    TO    NERVOrS   ACTION. 

§  25.  Of  tliese^  the  first  in  order  is  continuity  of  nerve- 
substance.  Disturbance  is  not  conveyed  from  end  to  end  of 
a  nerve  tliat  lias  been  cut  in  two ;  and  section  of  a  nerve- 
centre  similarly  prevents  tlie  transfer  of  an  impulse  from  one 
of  tbe  dissevered  parts  to  tlie  otlier. 

The  requisite  continuity  is  not  simply  the  continuity  of 
unbroken  contact :  there  must  be  continuity  of  molecular 
cohesion.  Placing  in  apposition  the  two  ends  of  a  divided 
nerve^  does  not  re-establish  nervous  communication.  Even 
when,  after  a  cut,  the  surrounding  flesh  has  been  healed,  it 
is  long  before  the  sundered  nerve-threads  re-unite  so  com- 
pletely that  they  transmit  stimuli  as  well  as  before. 

Further,  there  must  be  no  destruction  of  continuity  by 
molecular  disorganization.  Without  division  of  a  nerve,  and 
without  injury  of  its  sheath,  there  may  result  from  disease  a 
change  which  incapacitates  the  nerve-fibres — an  atrophy,  or 
a  breaking-vip  by  decomposition :  the  result  being  a  de- 
rangement of  those  lines  of  peculiar  nitrogenous  molecules 
which  receive  and  pass  on  the  waves  of  disturbance. 

§  26.  Nerve-structures,  whether  peripheral  or  central, 
permanently  disabled  as  they  are  by  actual  discontinuity, 
either  molar  or  molecular,  are  temporarily  disabled  by  dis- 
continuity of  molecular  ec^uilibrium.     Pressure  is  capable  of 


THE    CONDITIONS   ESSENTIAL   TO   NERVOUS    ACTION 


producing  re-arrangement  of  particles,  even  in  substances 
that  are  simple  and  comparatively  hard ;  as  is  shown  by  its 
power  of  altei'ing  the  direction  of  diamagnetic  polarity  in 
metals.  We  may  therefore  expect  that  in  substances  of  com- 
plex composition  and  little  cohesion,  pressure  will  readily 
cause  the  particles  to  change  their  relative  positions.  Hence 
there  is  no  difficulty  in  understanding  why  nerve-substance, 
having  a  balanced  molecular  structui'e  such  that  it  is  ever 
ready  to  pass  when  disturbed  from  one  of  its  isomeric  states 
to  the  other,  may  be  so  modified  by  pressure,  even  when 
small,  as  to  be  incapacitated  for  undergoing  these  alternate 
molecular  re-arrangements.  Be  this  as  it  may,  however,  the 
fact  is  that  one  of  the  conditions  to  nervous  action  is  ab- 
sence of  much  pressure. 

In  the  case  of  nerve-trunks,  demonstration  of  this  general 
truth  is  easy.  A  ligature  round  a  nerve  prevents  a  dis- 
turbance set  up  at  one  end  of  it  from  producing  any  effect 
at  the  other  end.  Partial  results  of  this  nature  are  familiar. 
By  external  pressure  on  a  limb,  the  conducting  power  of  the 
nerves  affected  is  much  diminished. 

That  pressure  on  the  centrally-seated  tracts  of  fibres, 
hinders  or  arrests  their  actions,  is  shown  in  every  case  of 
paralysis.  By  a  clot  of  blood  that  has  escaped  from  a 
ruptured  vessel,  or  by  a  quantity  of  lymph  that  has  oozed 
through  the  walls  of  capillaries  over-distended,  bundles  of 
fibres  at  the  base  of  the  brain,  or  in  the  spinal  cord,  are  un- 
duly squeezed ;  and  if  afferent  or  centripetal  fibres  they  cease 
to  bring  disturbances  from  the  periphery,  while  if  efferent 
or  centrifugal  fibres  they  cease  to  convey  impulses  to  the 
muscles. 

The  like  is  true  of  nerve-centres  as  wholes.  Indeed  pres- 
sure appears  to  be  a  greater  hindrance  to  their  actions  than 
to  the  actions  of  nerve-trunks.  That  certain  foi'ms  of  the 
abnormal  arrest  of  nervous  action  called  coma,  are  due  to 
excessive  congestion  of  the  blood-vessels  of. the  encephalon, 
seems  possible  ;  but  as  some  question  this  interpretation  wo 


70  THE    DATA   Or    PSYCHOLOGY. 

cannot  safely  base  an  inference  on  it,  Tliere  is,  however,  one 
conclusive  piece  of  evidence.  A  fracture  of  tlio  skull  that 
causes  indentation  over  a  considerable  area,  and  leaves  the 
bone  intruding  on  the  space  previously  filled  by  the  brain, 
stops  the  functions  of  the  brain — disturbances  sent  to  it 
call  forth  no  appropriate  co-ordinated  motions,  and,  indeed, 
no  motions  at  all.  But  when,  by  means  of  a  trephine,  the 
depressed  portion  of  bone  is  cut  out,  the  brain,  relieved  from 
pressure,  at  once  resumes  its  duties. 

Further  support  is  yielded  by  what  may  be  regarded  as 
converse  evidence.  If  excess  of  pressure  arrests  nerve- 
action,  and  if  the  normal  amount  of  pressure  allows  the 
normal  amount  of  nerve-action;  then  it  is  inferable  that 
nerve-disturbances  will  pass  with  undue  facility  if  the  pres- 
sure is  deficient.  Now  as  the  brain  is  contained  in  an  al- 
most-closed chamber  which  cannot  collapse,  it  follows  that 
if  the  cerebral  blood-vessels  are  rapidly  drained,  the  masses 
of  nerve-fibres  amid  which  they  ramify,  being  subject  to  less 
pressure  than  usual,  will  allow  waves  of  molecular  change  to 
pass  with  unusual  facility;  and  ordinary  impressions  pro- 
pagated to  the  centres,  will  produce  extraordinary  motor 
impulses.  Hence  the  seemingly-anomalous  fact  that  great 
loss  of  blood,  or  great  local  anaemia  caused  by  stoppage 
of  a  cerebral  artery,  causes  convulsions.  Such  a  result 
may  be  anticipated  as  the  first  result,  before  innutri- 
tion begins  to  tell ;  though  innutrition  will  afterwards 
cause  prostration  or  paralysis.  And  this  is  the  order  in 
which  the  phenomena  actually  occur.  The  like 

appears  true  of  the  peripheral  nervous  system.  The  afferent 
nerves  of  individuals  who,  though  otherwise  healthy,  have 
lax  tissues,  are  often  vmduly  impressible.  And  there  arc 
instances  of  undue  local  impressibility  which,  I  think,  admit 
of  this  interpretation.  It  has  been  found  that  an  arm 
rendered  anaemic  by  unnatural  constriction  of  its  arteries, 
thereby  reduced  in  tempei-ature  and  beginning  to  atrojDhy, 
may  nevertheless  have  its  afferent  nerves  affected  by  electric 


THE    CONDITIONS   ESSENTIAL   TO   NERVOUS    ACTION.  71 

discharges  in  an  unusual  degree.*  Deficient  pressure  on 
the  nerve-trunks  appears  a  possible  cause  of  this  otherwise 
strange  result. 

§  27,  Proof  that  heat  kept  aljove  a  certain  level  is  a  con- 
dition to  the  maintenance  of  nervous  action^  is  difficult  to 
disentangle  from  proof  that  the  maintenance  of  nervous 
action  depends  on  a  due  circulation  of  blood ;  for  the  one 
condition  is  usually  but  a  concomitant  of  the  other.  Never- 
theless, there  is  reason  to  infer  that  a  supply  of  free  mole- 
cular motion  is  requisite,  apart  from  a  supply  of  nutritive 
materials. 

The  general  fact  that  cold-blooded  animals  are  com- 
paratively inactive,  admits  of  the  interpretation  that  their 
low  temperature  is  due  to  their  inactivity,  as  "well  as  to  the 
interpretation  that  their  inactivity  is  a  consequence  of  their 
low  temperature ;  for  the  two  act  and  react  in  such  a  Avav 
that  neither  can  properly  be  called  the  cause  of  the  other. 
But  reptiles  w^hich  remain  quiescent  in  cold  ^veather,  and 
become  active  when  they  are  warmed  by  the  summer's  sun, 
yield  us  good  evidence.  Though  it  may  be  alleged  that 
their  greater  activity  arises  from  accelerated  circvilation  and 
aeration  of  the  blood,  yet  as  the  heart  and  lungs  are  set 
going  by  their  respective  nervous  centres,  we  must  infer 
that  the  warming  of  these  nervous  centres  by  external  heat, 
is  the  initial  change  in  these  animals  that  have  but  little 
power  of  producing  heat  by  their  own  actions.  In 

support  of  this  interpretation  may  be  cited  the  converse 
fact.  '\^^len  active  creatures,  capable  under  ordinary 
conditions  of  generating  enough  heat  within  themselves, 
are  exposed  to  conditions  under  w'hich  they  lose  heat  faster 
than  they  make  it,  their  nervous  actions  decrease,  and  they 
eventually  cease  to  move.     In  hybernating  mammals  w^e  sec 

*  I  am  indebted  for  this  fact  to  Dr.  Lastian,  who  observed  it  in  oiie  of  his 
own  patients. 


72  THE    DATA   OF    PSYCHOLOGY, 

an  annual  recurrence  of  this  relation  of  cause  and  effect ; 
and  in  mammals  that  do  not  hybernate^  as  in  ourselves,  it 
equally  holds  that  prolonged  exposure  to  extreme  cold  de- 
presses nervous  action,  causing  strong  tendency  to  sleep, 
and  that  death  results  if  the  bodily  temperature  is  allowed 
to  fall  still  lower. 

That  local  loss  of  heat  when  carried  far,  is  followed  by 
local  inaction  of  the  nerves,  is  shown  by  the  fact  that  parts 
of  the  body  that  have  been  greatly  cooled  down,  naturally 
or  artificially,  may  be  pricked  or  cut  or  pinched  without  any 
of  the  usual  distui^bances  being  conveyed  to  the  nerve- 
centres.  It  is  true  that  where  the  refrigeration  is  extreme, 
there  is  usually  a  partial  deprivation  of  blood ;  but  there 
is  evidence  that  when  this  is  not  the  case — when,  indeed, 
the  blood-vessels  are  congested,  as  in  red  hands  on  a  winter^s 
day,  loss  of  heat  entails  decuease  of  nerve-function.  That 
the  like  holds  of  the  respective  centres,  is  shown  by  the  use 
of  cold  as  a  therapeutic  agent :  ice  to  the  head  being  pre- 
scribed when  there  is  excessive  cerebral  action,  and  ice  to 
the  spine  being  a  means  of  diminishing  reflex  excitability. 

It  is  worth  remarking  that  this  dependence  of  nervous 
action  on  supply  of  heat,  yields  indirect  support  to  the  views 
set  forth  in  foregoing  chapters.  If,  as  was  inferred,  the 
disturbance  conveyed  along  a  nerve-thread  is  an  isomeric 
change,  during  which  some  molecular  motion  is  yielded  up 
by  each  molecule  as  it  passes  on  the  accumulated  wave  to 
its  neighbour — if  resumption  of  the  previous  isomeric  state 
implies  an  equivalent  absorption  of  molecular  motion  from 
surrounding  matter;  then,  in  proportion  to  the  heat  of 
surrounding  matter,  will  be  the  rapidity  with  which  the 
nerve-fibre,  resuming  this  previous  isomeric  state,  becomes 
fit  to  transmit  another  wave  of  molecular  change. 

§  28.  That  nerves  and  nerve-centres  act  only  so  long  as 
they  are  furnished  with  those  materials  which  the  blood- 
vessels bring  them,  is  a  familiar  truth.     The   quantity  of 


THE    CONDITIONS   ESSENTIAL   TO   NERVOUS    ACTION.  73 

blood  present  in  any  part,  and  the  rapidity  with  which  fresh 
blood  is  propelled  to  the  part,  both  affect  the  degree  of 
nervous  activity  in  the  part. 

Genei'al  depletion  is  a  cause  of  nervous  inaction :  if  the 
total  quantity  of  blood  in  the  body  is  much  diminished,  the 
great  nervous  centres  are  the  first  organs  to  feel  the  change. 
Temporary  loss  of  blood  produces  fainting,  or  sudden  arrest 
of  cerebral  action;  and  permanent  deficiency  of  blood  is 
accompanied  by  debility,  which  imphes  a  decreased  nervous 
discharge.  Supposing  that  no  blood  has  been  lost,  in- 
sensibility nevertheless  instantly  results  if  the  heart  ceases 
to  supply  the  brain  with  fresh  blood  in  place  of  the  blood 
it  contains.  Or  if  there  is  chronic  feebleness  of  the  hearths 
action,  there  is  proportionate  diminution  of  nervous  power. 
Where  the  total  quantity  of  blood  is  adequate  and  the  heart 
is  not  in  fault,  local  nervous  function  may  still  be  hindered 
by  local  anfemia,  resulting  from  aneurism  in  an  artery,  or 
from  what  is  called  an  embolism — a  plugging  up  of  an 
artery  with  coagulated  blood.  Thus  paralysis  is  caused  by 
embolism  of  the  cerebral  blood-vessel  which  supplies  the 
highest  part  of  the   motor  tract.  The  converse 

facts  similarly  imply  this  same  general  relation.  When, 
other  conditions  being  normal,  a  nerve-centre  is  highly 
charged  with  arterial  blood,  it  responds  with  unusual 
rapidity  to  the  disturbances  it  receives;  and  evolves  more 
than  ordinary  amounts  of  force,  shown  in  secondary  nervous 
changes,  or  in  muscular  motions,  or  both.  Supposing, 
again,  that  there  is  no  hyperaemia  of  a  nervous  centre,  it 
will  still  happen  that  if  the  heart  propels  blood  to  it  with 
unusual  rapidity,  its  libero-motor  function  will  be  exalted. 

At  the  periphery  of  the  nervous  system,  like  variations  of 
efficiency  follow  like  variations  of  circulation.  A  reduction 
in  the  quantity  of  blood  present,  caused  by  constriction  of 
the  vessels,  is  probably  one  cause  of  the  decreased  nervous 
impressibility  in  a  part  that  is  exposed  to  cold ;  and  to  the 
same  cause  is  perhaps  to  be  ascribed  some  of  the  comparative 


74  THE  DATA   OP    PSYCHOLOGY. 

sluggislincss  with  which  the  muscles  of  the  part  respond  to 
motor  impulses.  If  instead  of  local  lack  of  blood  there  is 
retardation  or  stoppage  of  the  local  current  of  bloody  the 
nerves  of  the  part  similarly  become  incapacitated  in  a  pro- 
portionate degree :  instance  the  blindness  that  results  from 
blocking  up  the  central  retinal  artery;  or  instance  the  gradual 
disappearance  of  impressibility  in  a  region  of  the  skin  that 
has  had    its    supplying    blood-vessel    tied.  Con- 

versely, excess  of  blood  around  the  peripheral  nerve-fibres, 
causes  unusual  excitability  of  them.  A  gentle  touch  on  the 
skin  in  its  normal  state,  sends  through  the  afferent  nerves  a 
disturbance  so  small  as  to  call  forth  from  the  central  organs 
scarcely  any  response;  but  where  the  skin  is  highh^  inflamed, 
a  like  touch  affects  them  so  much  that  the  disturbance,  when 
reflected  from  the  central  organs,  produces  a  start  of  the 
whole  body.  If  in  addition  to  local  excess  in  the  quantity 
of  blood  there  is  an  accelerated  flow  of  blood,  a  still  greater 
exaltation  of  local  nervous  action  follows.  It  is  a  familiar 
truth  that,  other  things  remaining  the  same,  an  inflamed 
part  is  made  more  irritable  by  anything  which  increases  the 
action  of  the  heart. 

§  29.  Nervous  action  depends  not  alone  on  the  quantity 
of  blood  supplied  but  also  on  its  quality — on  the  proportion 
of  the  needful  elements  contained  by  it.  , 
•  Genei'al  rather  than  special  warrant  must  suffice  for  this 
proposition.  Little  is  kno^vn  about  variations  in  the  consti- 
tution of  the  blood;  and  still  less  about  the  relations  between 
these  and  variations  of  nervous  activity.  That  a  blood 
greatly  impoverished,  as  in  dropsical  persons  (whose  tissues 
become  infiltrated  because  the  thin  serum  passes  too  easily 
through  the  walls  of  the  capillaries),  is  accompanied  by  ener- 
vation, is  pretty  clear;  and  we  can  scarcely  be  wrong  in 
concluding  that  a  blood  rich  in  the  constituents  of  nerve- 
substance,  renders  possible  a  great  evolution  of  nerve-force. 

But  there  is  indirect  evidence  serving  to  enforce  the  scanty 


THE    CONDITIONS    ESSENTIAL    T^lfE' 

direct  evidence.  For  we  have  abundant  proof  tbat  by  adding 
certain  matters  to  tbe  blood,  unusual  amounts  of  nervous 
action  may  be  evoked.  Alcobol,  nitrous  oxide,  tbe  vegeto- 
alkalies,  and  other  stimulants,  are  not,  indeed,  components 
of  nerve-substance ;  nor  is  there  any  reason  to  suppose  that 
they  can  serve  in  place  of  components.  Probably  their  im- 
mediate influence  is  that  of  setting  up  or  facilitating  the 
change  of  nerve- substance,  and  so  causing  unusual  disen- 
gagement of  molecular  motion.  But  by  showing  that  the 
supply  of  particular  substances  to  the  nervous  system  exalts 
nervous  activity,  they  make  it  more  manifest  that  nervous 
activity  must  partly  depend  on  the  supply  of  substances 
which  re-build  nerve-tissue  as  fast  as  action  disintegrates  it. 
We  must  not  omit  a  further  qualitative  character  of  a 
positive  kind.  The  blood  must  contain  oxygen.  What  is 
the  special  action  of  oxygen — whether  it  is  a  direct  disinte- 
grant  of  the  tissues,  including  nerve-tissue;  or  whether  it 
simply  facilitates  by  its  presence  molecular  disintegrations 
otherwise  caused ;  or  whether  it  serves  merely  to  combine 
with,  and  carry  away,  the  products  of  such  disintegrations 
otherwise  caused  ;  are  questions  about  which  there  are 
differences  of  opinion.  But  there  can  be  no  difference  of 
opinion  as  to  the  necessity  for  an  oxygenated  blood.  And 
opinions  can  scarcely  differ  respecting  the  general  relation 
that  exists  between  the  degree  of  oxygenation  and  the  de- 
gree of  nervous  activity. 

§  30.  While,  for  the  maintenance  of  nervous  action,  it  is 
requisite  that  certain  matters  shall  be  present  in  the  blood,  it 
is  also  requisite  that  certain  other  matters  shall  be  absent ; 
or,  to  speak  strictly,  that  they  shall  be  present  in  but  small 
proportions.  These  are  the  compounds  resulting  from  de- 
composition of  the  tissues — the  nervous  tissue  included.  The 
two  most  important  are  cai-bonic  acid  and  urea. 

If  the  exhalation  of  carbonic  acid  by  the  lungs  is  greatly 
retarded,  lethargy  ensues :    disturbances  at   the  periphery 


76  THE    DATA   OP   PSYCHOLOGY. 

of  the  nervous  system  fail  to  call  forth  the  usual  responses. 
If  the  exhalation  is  completely  arrested,  complete  insensi- 
bility is  soon  produced ;  followed  quickly  by  arrest  of  the 
inferior  nervous  functions,  and  consequently  of  all  other 
functions.  And  these  effects  arise  still  more  rapidly  if  there 
is  an  absorption  of  carbonic  acid  through  the  lungs,  instead 
of  an  arrested  excretion  of  the  carbonic  acid  internally 
generated. 

In  an  analogous  but  less  rapid  manner,  a  decrease  and 
final  stoppage  of  nervous  action  is  caused  by  an  accumula- 
tion in  the  blood  of  urea,  or  of  those  nitrogenous  products 
represented  by  it.  If  the  kidneys  fail  to  perform  their  func- 
tion, or  if  the  waste  nitrogenous  products  which  they  have 
separated  from  the  blood  are  prevented  from  escaping  out  of 
the  body,  and  are  re-absorbed ;  there  results  a  nervous  in- 
action, ending  presently  in  coma  and  finally  in  death. 

§  31.  Such,  stated  as  fully  as  is  needful  here,  are  the  con- 
ditions essential  to  nervous  action.  Qualifications  have  been 
passed  over;  and  much  evidence  has  been  omitted.  In 
summing  up  these  leading  facts  which  alone  concern  the 
psychologist,  we  may  with  advantage  observe  how  they 
harmonize  with  the  general  views  of  nerve-sti'ucture  and 
nerve-function  set  forth  in  foregoing  chapters.  All  these 
pre-requisites  to  nervous  action  obviously  admit  of  being 
grouped  as  pre-requisites  to  the  genesis  of  molecular 
motion,  and  pre-requisites  to  the  conveyance  of  molecular 
motion. 

That  molecular  motion  may  be  disengaged  there  must  be 
decomposition;  and,  therefore,  for  the  discharge  of  molecular 
motion  to  be  maintained,  decomposition  must  be  facilitated. 
The  quantity  of  waste  being  a  measure  of  the  quantity  of 
force  evolved,  it  follows  that  the  nervous  s^ystem  requires 
a  good  supply,  and  quick  exchange,  of  blood ;  since  in  the 
blood  are  brought  the  matters  that  favour  disintegration. 
Similarly    with    respiration,    considered    as    a    process    of 


THE   CONDITIONS   ESSENTIAL  TO  NERVOUS   ACTION.  77 

absorbing  tliat  oxygen  wliicli  directly  or  indirectly  aids 
tlie  metamorphosis.  And  so  likewise  witli  tlie  excre- 
tion of  those  -waste  products  wliicli  hinder  the  metamor- 
phosis. But  perpetual  waste  must  be  met  by 
perpetual  repair.  If  its  action  is  to  continue^  nervous  tissue 
must  be  re-composed  as  fast  as  it  is  decomposed.  Hence 
the  reason  why  there  is  needed  a  blood  that  is  rich  in  nerve- 
constituents.  Hence  the  fact  that  abundant  blood  must  be 
present  wherever  there  is  much  nervous  action.  And  hence^ 
alsOj  the  necessity  for  an  efficient  circulation  to  replace  by 
fresh  blood,  the  blood  that  has  been  used. 

Equally  well  do  the  several  conditions  essential  to  the 
transmission  of  nervous  disturbance,  conform  to  the  hypo- 
thesis that  the  disturbance  transmitted  is  a  wave  of  isomeric 
change.  For  if  it  is,  we  at  once  see  why  there  must  be 
not  merely  contact-continuity  of  nerve-fibre,  but  molecular 
continuity.  We  are  helped  to  understand  how  pressure,  by 
deranging  that  delicate  molecular  balance  which  makes 
possible  the  alternation  of  isomeric  states,  may  prevent 
the  passage  of  nervous  discharges.  And  we  are  supplied 
with  an  explanation  of  the  fact  that  the  presence  of  free 
molecular  motion  or  heat,  is  needful  to  enable  a  nerve  con- 
tinually to  resume  its  fitness  for  conveying  a  wave  of  change. 

Before  closing  the  chapter  it  should  be  pointed  out  that 
these  many  conditions  essential  to  nervous  action,  are  never 
all  fulfilled  at  one  time  in  the  same  degree,  but  are  usually 
fulfilled  in  various  degrees  and  combinations ;  and  that  by 
npw  conspiring  and  now  conflicting,  they  produce  results 
that  are  complicated  and  often  perplexing.  Thus,  for  in- 
stance, substances  which  directly  stimulate  the  nervous 
system,  are  usually  substances  which  retard  the  exchange 
of  gases  in  the  lungs,  and  by  so  doing  depress  the  state 
of  the  nervous  system;  and  these  conflicting  actions,  diffe- 
rent in  their  proportions  in  different  individuals,  and  in  the 
same  individual  at  different  times,  often  work  opposite 
effects,  or  work  first  one  effect  and  then  the  other.     Again, 


78  THE    DATA   OF   PSYCHOLOGY. 

ricliness  of  blood,  by  facilitating-  liigh  nutrition  of  nerye- 
centres,  conduces  to  nervous  activity.  Yet  there  is  a 
plethoric  state  whicli  is  not  nervously  active ;  and  starva- 
tion, with  its  greatly  impoverished  blood,  has  a  phase  at 
which  delirium  sets  in,  in  consequence  of  the  unduly  rapid 
disinteo'ration  of  the  nerve-centres.  Analoofous  incongruities, 
too  numerous  to  specify  here,  continually  occur.  This  en- 
tanglement of  the  conditions  must  be  borue  in  mind  and 
allowed  for  in  each  case. 


CHAPTER  Y. 

NERVOUS    STIMULATION   AND    NERVOUS    DISCHARGE. 

§  32.  Every  agent  capable  of  altering  the  molecular  state 
of  a  nerve^  causes  the  nerve  to  produce  the  particular  change 
which  it  habitually  produces.  Experiments  prove  that  each 
nerve  is  made  to  work  the  same  kind  of  effect  by  stimuli  of 
all  orders ;  or^  to  speak  strictly,  it  is  found  that  the  effect  is 
of  the  same  kind  wherever  its  kind  renders  it  accessible  to 
observation. 

Thus,  if  an  exposed  end  of  a  nerve  which  goes  to  a 
muscle  is  roughly  touched,  the  muscle  contracts.  If  it  is 
eroded  by  an  alkali  or  an  acid,  the  muscle  contracts.  If  it 
is  galvanized,  the  muscle  contracts.  If  it  is  suddenly  heated, 
still  the  muscle-  contracts.  Similarly  with  a  vaso-motor 
nerve.  No  matter  whether  the  disturbini?  ao^ent  be  me- 
chanical,  chemical,  thermal,  or  electric,  there  results  at  the 
peripheral  extremity  a  like  change  in  the  state  of  the  ad- 
jacent arteries. 

An  allied  truth  is  that  whether  a  nerve  be  irritated  at  the 
end  which  normally  receives  the  disturbance,  or  whether  it 
be  irritated  at  some  place  between  this  and  the  organ  acted 
upon  by  it,  the  effects  wrought  are  alike — in  nature,  at 
least,  if  not  in  degree.  As  already  said,  the  quautitij  of 
change  set  up  increases  Avith  the  length  of  the  nei've  through 
which  the  impulse  is  transmitted.     But  the  quality  of  this 


80  THE    DATA   OF    TSYCHOLOGY. 

cTiange  remains  identical  bo  the  stimulus  applied  at  a  near 
point  or  a  remote  point. 

This  last  truth,  equally  Avith  the  first,  harmonizes  with  the 
supposition  on  which  we  have  thus  far  proceeded.  If  the 
disturbance  that  ti-avels  along  a  nerve  is  a  wave  of  isomeric 
transformation,  the  kind  of  effect  produced  by  the  wave  at 
the  place  it  eventually  reaches,  will  bo  the  same  whatever 
stimulus  set  it  up,  or  wherever  it  commenced. 

§  33.  Nerve  is  not  capable  of  continuous  stimulation  or 
continuous  discharg'o.  Persistent  action  of  whatever  kind 
on  a  nerve-termination  or  the  cut  end  of  a  nerve,  doea  not 
produce  a  persistent  effect  on  the  connected  nerve-centre,  or 
on  the  connected  peripheral  organ. 

Supposing  the  nerve  supplying  some  muscle  has  been  dis- 
sected out  and  cut  in  two ;  then,  if  the  exposed  part  be  sud- 
denly pressed  the  muscle  will  suddenly  contract ;  but  main- 
tenance of  the  pressure  will  not  cause  maintenance  of  the 
contraction.  Or  if  this  nerve  is  made  part  of  an  electric 
circuit,  then,  at  the  moment  of  completing  the  circuit,  the 
muscle  will  contract ;  but  its  contraction  is  only  momentary, 
and  the  subsequent  continuance  of  the  current  works  no 
visible  effect.  To  keep  up  muscular  contraction,  it  is  requi- 
site to  send  through  the  nerve  a  quick  succession  of  separate 
disturbances.  If  the  nerve  forms  part  of  an  electric  circuit 
in  which  there  is  an  apparatus  for  breaking  and  completing 
the  circuit ;  then,  at  each  completion  of  the  circuit,  the 
muscle  "contracts  ;  and  when  the  alternate  breaks  and  com- 
pletions follow  one  another  very  rapidly,  the  contraction  of 
the  muscle  becomes  practically  jDcrsistent.  This  truth  is 
demonstrable  by  experiment  on  a  dead  frog,  and  also  by 
experiment  on  the  living  human  subject.  A  man  who 
grasps  the  two  metallic  cylinders  forming  the  poles  of  a 
magneto-electric  machine,  cannot  leave  hold  of  the  cylinders 
when  the  intermittent  current  is  passed  through  his  arms. 
The  like  result  occurs  when  the  disturbances  are  mechanical 


NERVOUS    STIMULATION   AND   NERVOUS   DISCHARGE.  81 

instead  of  electric.  If  the  cut  end  of  a  motor  nerve  is  sub- 
ject to  a  rapid  series  of  taps,  the  muscle  it  supplies  is 
thrown  into  a  state  of  tetanus. 

The  fact  that  the  so-called  nerve-current  consists  of 
successive  pulses,  is  one  of  great  significance.  '"We  shall 
find  hereafter  that  it  has  many  important  corollaries.  For 
the  present  it  will  sufiice  to  observe  how  entirely  congruous 
it  is  with  the  hypothesis  on  which  we  have  thus  far  pro- 
ceeded. If  a  nervous  disturbance  travels  as  a  wave  of  mole- 
cular change — if  this  wave  is  such  that  the  molecules  of 
nerve-substance  fall  from  one  of  their  isomeric  states  to  the 
other ;  then,  having  fallen  in  passing  on  and  increasing  the 
pulse  or  shock,  they  remain  incapable  of  doing  anything 
more  until  they  have  resumed  their  previous  isomeric  state. 
Hence  the  very  nature  of  the  process  necessitates  the  inter- 
mittent character  of  nerve-action. 

§  34.  The  transmission  of  a  disturbance  through  a  nerve 
takes  an  appreciable  time.  The  rate  of  transmission,  as 
measured  by  Professor  Helmholtz,  has  been  found  to  vary 
from  about  28  yards  per  second  to  32  yards  per  second. 
Difierence  of  constitution  is  doubtless  the  cause  of  this 
variation — a  variation  to  which  is  due  that  individual  pecu- 
liarity recognized  by  astronomers  in  what  they  call  "  the 
personal  equation." 

This  peculiarity  afibrds  yet  another  confirmation  of  the 
belief  that  a  nervous  discharge  is  a  wave  of  isomeric  trans- 
formation. If  the  disturbance  propagated  through  any 
series  of  molecules  is  one  that  does  not  permanently  change 
their  relative  positions ;  then  the  transfer  of  the  disturbance 
may  be  excessively  rapid,  because  the  amount  of  molecular 
momentum  to  be  generated  is  excessively  minute.  But  if  the 
molecules  have  to  be  transposed — if,  as  in  isomeric  transfor- 
mation, the  components  of  each  compound  molecule  have  their 
relative  positions  altered;  then  the  quantity  of  molecular 
momentum  generated  must  be  comparatively  very  large; 
6 


82  THE    DATA   OF   PSYCHOLOGY. 

and  as  the  genesis  of  this  momentum  takes  place  in  each 
molecule  before  the  next  is  affected,  the  transfer  of  the 
disturbance  must  be  greatly  retarded.* 

•  Perhaps  too  much  has  already  been  said  respecting  the  nature  of 
nerve-action.     But  before  finally  leaving  the  subject,  I  must  add  some 
important    illustrative    facts    that   have   come    to   my   knowledge    while 
writing  this  chapter.  They  are  contained  in  a  paper  by  Mr.  Gore,  published 
in  the  Transactions  of  the  Boy al  Society  for  1S58,  describing  the  allotropic 
changes  undergone  by  electro-deposited   antimony.      Antimony   so   depo- 
sited assumes,  according  to  the  conditions,  two  forms — a  dark,  amorphous, 
or  unstable  form  ;  and  a  grey,  crystalline,  or  stable  form.     When  a  mass  of 
the  amorphous  antimony  is  disturbed  at  one  end,  there  begins  a  change 
into  the  crystalline  antimony,  which  spreads  almost  instantly  throughout 
the  whole  mass,  with  great  evolution  of  heat.     A  slight  tap  with  a  hard 
substance  suffices  to  initiate  this  transformation.      Touching   one   of  the 
angles  with  a  hot   body   equally   produces   the   effect.      And  it   is  also 
produced  by  an  electric  spark.      A  temperature   below  that   of   boiling 
water  sufficed  to  cause  the  change  ;  and  Mr.  Gore  found  that  in  proportion 
as  the  whole  mass  was  raised  towards  this  temperature,  the  metamorphosis, 
more  easily  set  up,  travelled  with  greater  rapidity.     When  a  copper  wire 
was  coated  with  a  film  of  this  amorphous  antimony,  the  allotropic  change 
progressed  along  it   at  a  rate  varying  from    12  to  30  feet   in   a  minute. 
Absorption  of  the  evolved  heat  by  the  copper  wire,  was  found  to  be  the 
cause  of  retardation  when  the  change  advanced  slowly  ;  whence  it  follows 
that  were   none  of   the  disengaged  heat  allowed  to  escape,  the  wave  of 
change   would   travel   much   faster.      A   further    significant   fact   is  that 
when  this  transformation  was  propagated  through  some  amorphous  anti- 
mony that    had  been    previously   reduced    to    powder,    part    of    it  was 
oxidized — the  disturbance  caused  by  the  allotropic  change  initiated  chemical 
change,i>  in  parts  of  the  substance  that  were  favourably  circumstanced  for 
chemical  change.     See  then  the  parallelism.     We  have  the  transformation 
set  up  indifferently,  as  in  nerve,  by  mechanical  force,  heat,   electricity. 
We  have  it  facilitated,  as  in  nerve,  by  raised  temperature.     We  have  it 
travelling  from  end  to  end  of  a  mass  with  a  velocity  which,  though  far  less 
than  that  of  the  nerve-wave,  is  still  considerable.     And  we  have  allotropic 
change  initiating   chemical  change,   just   as  we   concluded  that  isomeric 
change  in  a  nerve-fibre  sets  up  chemical  change  in  a  nerve-vesicle.     Let 
me  not  omit  an  interpretation  of  nerve- structure,  which  is  suggested  by 
Mr.  Gore's  experience  that  the  transmission  of  the  allotropic  change  is 
rapid  in  proportion  as  the  evolved  heat  is  retained.     In  developed  animals, 
nerve- fibres  are  surrounded  by  sheaths  of  medullary  matter  ;  and  we  saw 
reasons  for  concluding  that  this  medullary  matter  is  an  insulator.     Now 
it   has  recently   been   discovered    that   white   or  fibrous    nerve-tissue,  is 
chemically    distinguished    from    grey   or    vesicular  nerve-tissue,   by   the 


KEKVOUS    STIMULATION   AND   NEEYOUS    DISCHARGE.  83 

§  35.  Allied  witli  tlie  fact  that  a  nerve- disturbance  takes 
an  appreciable  time  to  travel  from  periphery  to  centre  or 
from  centre  to  periphery,  is  the  fact  that  the  effect  produced 

presence  in  large  quantity  of  a  substance  called  2^^'otago7i ;  and  this  sub- 
stiince  proves  to  be  of  excessively  complex  composition — has  a  molecule 
more  highly  compounded  than  any  other  known  molecule.  But  in  pro- 
portion as  molecules  become  complex  and  large,  the  masses  formed  of 
them  become  bad  conductors  of  molecular  motion.  It  is  inferable,  then, 
that  the  essential  nerve-fibre  is  imbedded  in  a  substance  especially  distin- 
guished by  inability  to  absorb  the  molecular  motion  disengaged  during  the 
isomeric  change  of  the  nerve-fibre. 

I  have  hitherto  passed  over  without  remark,  the  hj'pothesis  at  one  time 
current,  and  still  surviving  in  some  minds,  that  the  nervous  force  is  either 
electricitj'^  or  some  form  of  force  allied  to  it.  In  addition  to  the  many 
foregoing  reasons  for  adopting  another  hypothesis,  it  may  be  well  to  set 
down  here  the  reasons  for  rejecting  this.  The  highest  rate  of  the  nervous 
discharge  is  some  32  yards  per  second.  The  electric  discharge  travels  at 
the  rate  of  280,000  miles  per  second.  The  one  velocity  is  thus  nearly 
16,000,000  times  the  other.  That  a  force  allied  to  the  electric  should  have 
a  velocity  so  enormously  different,  seems  very  unlikely.  Again,  an  electric 
current,  so  long  as  its  source  is  unexhausted  and  the  circuit  unbroken, 
is  a  continuous  current ;  but  the  nerve-current  is  not  continuous.  Hence 
if  the  nerve-force  is  of  a  kind  allied  to  the  electric,  its  mode  of  alliance  is 
quite  exceptional  ;  for  the  other  allied  forces,  heat,  light,  and  magnetism, 
are  not  intermittent.  Once  more,  nervous  transmission  is  facilitated  by 
heat ;  whereas  heat  is  an  obstacle  to  electric  transmission,  and  diminishes 
or  destroys  magnetic  action.  The  fact  is  that  but  for  the  accidental 
observation  of  Galvani,  the  suspicion  that  the  nerve-force  is  electric  or 
quasi-electric,  would  probably  never  have  been  entertained  ;  and  it  should 
have  been  abandoned  as  soon  as  it  was  found  that  other  disturbing  agents, 
physical  and  chemical,  work  just  the  same  effects.  The  conception  has, 
indeed,  been  kept  alive  by  the  discovery  that  electricity  is  generated  by 
certain  fishes.  But  the  supposed  support  is  wholly  imaginary.  If  because 
the  Torpedo  evolves  electricity  by  the  help  of  nerves  ramifying  through  its 
electric  organ,  it  is  inferred  that  the  nerve-force  is  electricity  ;  it  may  in 
like  manner  be  inferred  that  the  nerve-force  is  sensible  motion,  because  it 
generates  sensible  motion  in  muscles.  But,  it  may  be  asked,  do  not  the 
experiments  of  Du  Bois-Reymond  j'ield  support  to  the  hypothesis  ?  A 
very  doubtful  support  I  think.  The  phenomena  he  describes  may  well 
be  merely  incidental  accompaniments  of  actions  that  are  in  themselves 
neither  electric  nor  quasi-electric.  The  truth  that  both  molar  and 
molecular  changes  in  the  distribution  of  matter  habitually  destroy  the 
electric  equilibrium,  would  be  a  sufficient  general  justification  for  this 
belief.     "But  there  is  a  special  justification.     Direct  proof  exists  that  the 


84  THE   DATA   OF   PSYCHOLOGY. 

at  the  centre  or  at  tlie  periphery  lasts  an  appreciable 
time.  That  muscular  contraction  is  continuous  though  the 
stimulus  is  intermittent,  goes  to  show  this.  The  genesis 
of  molecular  modification  in  muscle  by  the  molecular  modi- 
fication in  the  nerve-fibres  permeating  it,  has  a  duration 
that  bridges  the  interval  between  each  pulse  of  stimulus 
and  the  next.  We  have  no  direct  proof  that  a  like  con- 
tinuity of  state  results  from  the  successive  waves  propa- 
gated to  a  nerve-centre;  for  the  actions  of  which  nerve- 
centres  are  the  seats  are  not  objectively  perceptible.  But 
we  shall  presently  find  abundant  indirect  proof  that  these 
changes  also  last  for  measurable  periods. 

This  general  truth,  like  its  predecessor,  may  be  regarded 
as  a  corollary  from  what  has  gone  before.  The  transforma- 
tions classed  as  chemical  take  time,  equally  with  those 
classed  as  isomeric.  It  is  true  that  explosions  due  to 
chemical  action  are  what  we  call  instantaneous  (a  descrip- 
tion of  them  which  is  not,  however,  scientifically  accurate ; 
as  may  be  perceived  when  the  matter  exploded  is  of  con- 
particular  kind  of  molecular  change  we  have  supposed  to  take  place  in 
nerve,  and  in  muscle,  is  adequate  to  produce  the  phenomena  observed  by 
Du  Bois-Reymond.  Mr.  Gore  found  that  if  a  copper-wire,  coated  with 
amorphous  antimony,  formed  part  of  an  electric  circuit,  it  happened  that 
whenever  the  allotropic  change  propagated  along  the  antimony  stopped,  the 
galvanometer-needle  was  deflected.  Now,  since  during  the  maintenance  of 
a  muscular  contraction,  nerve-pulses  are  continually  arriving  and  ceasing, 
and  the  muscular  fibres  (never  all  in  action  together)  are  at  every  instant 
some  of  them  contracting  and  some  relaxing,  it  follows  that  there  will  be  a 
succession  of  stoppages  of  isomeric  changes.  Consequently  there  will  be  a 
maintenance  of  deflection  in  the  galvanometer  if  a  contracted  muscle  forms 
part  of  the  electric  circuit. 

[Since  this  note  has  been  in  type,  I  have  referred  to  the  lecture  delivered 
by  M,  Du  Bois-Reymond  at  the  Eoyal  Institution  on  April  13,  1S66, 
"On  the  Time  required  for  the  Transmission  of  Volition  and  Sensation 
through  the  Nerves,"  for  the  purpose  of  verifying  one  of  the  statements 
above  made  ;  and  I  find  that  at  the  close  of  this  lecture  he  goes  a  long  way 
towards  abandoning  his  hypothesis.  Though  he  says  "  it  would  be  rash,  as 
the  matter  stands,  entirely  to  dismiss  the  notion  of  electricity  being  con- 
cerned ;"  and  though  he  sketches  out  a  theory  of  nerve-composition  such  as 
makes  it  conceivable  that  an  electric  disturbance  might  travel  along  a  nerve 


NERVOUS  STIMULATION  AND  NERVOUS  DISCHARGE.     85 

siderable  bulk) .  But  explosions  occur  only  in  tliose  excep- 
tional cases  where  tlie  elements  concerned  are  eitlier_,  as  in 
detonating  compounds,  distributed  among*  one  another 
molecularly,  or,  as  in  gunpowder,  with  minute  intimacy. 
In  ordinary  cases,  where  sensible  masses  of  the  elements 
concerned  are  external  to  one  another,  the  chemical  actions, 
limited  to  the  surfaces  of  contact,  proceed  with  compara- 
tive slowness.  Now  the  granular  protoplasm  contained 
in  and  around  nerve-vesicles,  forms,  with  its  permeating 
liquids  and  the  blood  in  adjacent  capillaries,  a  mass  of 
which  the  corEiponents  are  but  imperfectly  interfused;  and 
therefore  a  chemical  change  cannot  pass  through  it  in- 
stantly. Hence  between  the  reception  of  a  pulse  of  mole- 
cular motion  by  a  nerve-centre,  and  the  emission  of  a  gush 
of  molecular  motion,  or  discharge,  some  little  time  must 
elapse. 

^  30.  If  a  nerve-centre  that  receives  a  stimulus  through 
an  incoming  nerve,  undergoes  a  chemical  change  and  sends 

at  the  observed  rate  (basing  this,  however,  on  the  gratuitous  assump- 
tion that  the  molecules  of  nerve-matter  have  north  and  south  poles)  ;  yet 
he  admits  that  much  evidence  points  another  way.  He  saj's  that  "to 
identify  it  (the  nervous  agent)  with  the  electric  current  as  it  circulates  in  a 
telegraph-wire  must  appear  hopeless,  even  if  a  circuit,  such  as  would  be 
necessary  for  the  supposed  nerve  current  to  circulate  in,  were  anatomically 
demonstrated.  Thus  to  the  other  arguments  against  this  view  of  the 
nervous  agent — that  the  resistance  of  the  nerve-tubes  would  be  far  too 
great  for  any  battery  to  send  an  available  current  through  them — that  the 
physiological  insulation  of  the  nerve-tubes  from  each  other  would  be  im- 
possible to  explain — that  the  effect  of  ligature  or  of  cutting  the  nerve  and 
causing  its  ends  to  meet  again,  would  be  equally  obscure — to  these  argu- 
ments, unanswerable  as  they  are  in  themselves,  the  researches  sketched  in 
this  lecture  have  added  corroborative  evidence  of  the  highest  order.  What 
we  have  termed  the  nervous  agent,  if  Ave  look  upon  its  very  small  velocity, 
in  all  probability  is  some  internal  motion,  perhaps  even  some  chemical 
change,  of  the  substance  itself  contained  in  the  nerve-tubes,  spreading  along 
the  tubes,  according  to  the  speaker's  experiments,  both  ways  from  any 
point  where  the  equilibrium  has  been  disturbed ;  being  capable  of  an 
almost  infinite  number  of  variations  or  gradations,  and  of  so  peculiar  a 
character  as  to  require  the  unimpaired  condition  of  the  nervous  structure."] 


Sft  THE    DATA   OF   PSYCHOLOGY. 

a  discharge  along  out-going  nerves^  it  tliereupon  becomes 
less  capable  of  emitting  sucb  discbarges  in  response  to  sucb 
stimuli.  The  quantity  of  molecular  motion  locked  up  in  a 
nerve-centre,  is  measured  by  tbe  contained  quantity  of 
unstable  nerve-matter;  and  decomposition  of  tbat  part  of 
tbe  unstable  nerve-matter  vrbicb  was  most  favourably 
placed  for  being  acted  on_,  leaves  not  only  a  diminished 
quantity  but  a  quantity  tbat  is  less  favourably  placed  for 
being  acted  on — leaves,  therefore,  a  decreased  readiness  to 
undergo  change  when  disturbed,  as  well  as  a  decreased 
stock  of  molecular  motion  to  be  liberated.  Consequently, 
other  things  remaining  the  same,  every  excitation  of  a 
nerve-centre  reduces,  for  a  time,  its  imj)ressibility  and  its 
energy. 

This  temporary  enfeeblement  of  a  nerve-centre,  when 
caused  by  moderate  action,  is  inconspicuous.  The  disinte- 
grated mass  quickly  re-integrates  itself  from  the  materials 
brought  by  the  blood.  But  if  the  stimulation  and  con- 
sequent discharge  are  violent,  or  if  stimulations  and  dis- 
charges are  repeated  very  rapidly,  then  repair  falls  so  far  in 
arrear  of  waste  that  partial  or  entire  incapacity  of  the 
nerve-centre  results.  All  its  unstable  svibstance  within 
easy  reach  of  in-coming  disturbances  has  been  decomposed; 
leaving  such  part  only  of  its  unstable  substance  as  is  most 
removed  from  disturbances,  and  can  be  affected  only  by 
excessive  ones.  A  well-known  experiment  on  the  vaso- 
motor system  of  a  frog,  may  be  cited  in  illustration.  If  a 
frog's  foot  be  placed  under  a  microscope,  and  so  adjusted 
that  the  arteries  ramifying  through  the  transparent  mem- 
brane between  the  toes  are  brought  into  view,  then,  if  a 
jDowerful  irritant  be  applied  to  this  membrane,  the  first  re- 
sult observed  is  that  these  arteries  are  violently  constricted 
— the  strong  impression  conveyed  to  the  vaso-motor  centres 
there  liberates  an  excessive  discharge  along  the  fibres 
supplying  these  arteries,  causing'  spasmodic  contractions  of 
their  muscular    coats.      The  second  result   is   that   these 


NERVOUS    STIMULATION   AND   NERVOUS    DISCHARGE.  87 

arteries  dilate  :  losing  tlicir  normal  contractility  thoy 
become  distended  with,  blood,  and  tbe  part  is,  as  we  say, 
congested.  That  this  is  due  to  extreme  prostration  or  tem- 
porary paralysis  of  the  vaso-motor  centre,  has  been  clearly 
proved;  for  if  tlie  nerve-trunk  containing  the  vaso-motor 
fibres  be  dissected  out  and  artificially  irritated,  the  dilated 
arteries  instantly  contract.  How  a  nerve-centre  may  be 
prostrated  by  a  rapid  succession  of  moderate  stimuli  and 
discharges,  instead  of  by  one  violent  stimulus  and  discharge, 
is  shown  by  the  familiar  effect  of  friction  on  the  human  skin. 
A  single  moderate  rub  causes  only  a  slight  reflex  action  on 
its  vessels,  and  leaves  the  vaso-motor  apparatus  ready  to 
act  afresh  with  no  apparent  diminution  of  power.  But  a 
series  of  rubs  is  followed  by  temporary  congestion  of  the 
vessels  :  it  is  some  little  time  before  the  vaso-motor  centre 
regains  its  full  control  over  them.  And  if  the  skin  be 
continuously  chafed,  the  excessive  waste  and  debility  of 
the  vaso-motor  centre  entail  that  enduring  redness  called 
congestion.  Those  parts  of  the  nervous  system  con- 
cerned in  muscular  action,  daily  illustrate  the  same  general 
relation.  Fatigue  is  a  state  in  which  the  ability  to  generate 
motion  has  been  greatly  diminished  by  long-continued 
genesis  of  motion ;  and  every  tired  horse  skews,  by  the 
small  response  he  makes  to  a  cut  of  the  whip,  that  a  more 
violent  impulse  must  be  propagated  to  the  nerve-centres  to 
cause  the  ordinary  evolution  of  nervous  energy. 

Irregularities  in  the  manifestation  of  this  truth,  are  due  to 
that  entanglement  of  the  conditions  which  was  indicated  at 
the  close  of  the  last  chapter.  It  frequently  happens,  for 
instance,  that  after  performing  its  function  for  some  time, 
a  nerve-centre  responds  to  the  demands  on  it  better  than  at 
first — a  fact  apparently  at  variance  with  the  foregoing  con- 
clusion. ■  But  this  conclusion  supposes  all  the  circumstances 
to  have  remained  the  same;  and  in  such  cases  they  have  not 
remained  the  same.  There  has  been  an  exaltation  of  the 
heart's  action,  or  a  local  increase  in  the  quantity  of  blood,  or 


88  THE    DATA   OF   PSYCHOLOGY. 

a  more  rapid  aeration  of  blood,  or  all  of  these.  When  every 
appliance  which  furthers  the  disintegration  and  re-integra- 
tion of  a  nerve-centre,  has  been  brought  into  full  play,  both 
waste  and  repair  go  on  faster;  and  there  result  greater 
impressibility  aud  energy  than  when  the  previously-unused 
centre  contained  but  little  blood  languidly  circulating. 

§  37.  Were  Life  uniform  in  its  rate — were  terrestrial  con- 
ditions such  that  actions  of  all  kinds  could  be  performed  as 
readily  at  one  time  as  at  another,  repair  and  waste  of  all 
organs,  including  nervous  organs,  would  have  to  keep  an  ap- 
proximately-even pace,  one  with  the  other.  But  the  alterna- 
tion of  day  and  night  entails  an  alternation  of  greater  and  less 
facility  for  actions  ;  and  there  has  resulted  in  organisms  an 
adapted  alternation  in  the  relative  rates  of  waste  and  repair. 
The  adaptation  is  manifestly  due  to  survival  of  the  fittest. 
An  animal  so  constituted  that  waste  and  repair  were  balanced 
from  moment  to  moment  throughout  the  twenty-four  hours, 
would,  other  things  equal,  be  overcome  by  an  enemy  or 
competitor  that  could  evolve  greater  energy  during  the 
hours  when  light  facilitates  action,  at  the  expense  of  being 
less  energetic  during  the  hours  of  darkness  and  concealment. 
Hence  there  has  necessarily  established  itself  that  rhythmical 
variation  in  nei'vous  activity,  which  we  see  in  sleep  and 
waking.  Let  us  observe  how  these  are  interpretable,  the 
one  as  a  state  of  the  nervous  centres  in  which  waste  has  got 
considerably  in  excess  of  repair,  and  the  other  as  a  state  in 
which  repair  has  made  up  for  previous  excess  of  waste. 

Confining  ourselves  to  persons  whose  functional  rhythms 
have  not  been  deranged  by  undue  excitements,  we  see  that 
after  some  sitxeen  or  eighteen  hours  of  sustained  impressi- 
bility and  energy,  there  is  a  diminished  readiness  to  respond 
to  stimuli  that  fall  on  the  eyes,  ears,  and  surface  of  the  body 
at  large ;  and  presently  this  becomes  so  pronounced  that 
loud  sounds  and  the  irritations  produced  by  strained  atti- 
tudes, fail  to  evoke  movements.     When  great  exertion  has 


NERVOUS    STIMULATION   AND   NEKVOUS   DISCHARGE.  89 

Tseen  goue  tlirougli,  or  wlien  previous  intervals  ot  sleep 
have  been  omitted,  the  decrease  of  impressibility  is  such 
that  tickling  the  nostrils  or  pinching  the  skin  does  nothing 
more  than  cause,  perhaps,  a  reflex  start.  This  change,  so 
marked  and  often  so  rapidly  established,  seems  greater  than 
the  alleged  cause  can  produce ;  but  it  is  fully  accounted  for 
when  we  include  an  indirect  effect  of  this  cause.  The  waste 
of  the  nerve-centres  having  become  such  that  the  stimuli 
received  from  the  external  world  no  longer  suffice  to  call 
forth  from  them  adequate  discharges,  there  results  a  di- 
minished impulse  to  those  internal  organs  which  subserve 
nervous  activity,  including,  more  especially,  the  heart. 
Consequently  the  nerve-centres,  already  working  feebly^ 
are  supplied  with  less  blood  and  begin  to  work  more  feebly — 
respond  still  less  to  impressions,  and  discharge  still  less  to 
the  heart.  And  so  the  two  act  and  re-act  until  there  is 
reached  this  state  of  profound  unimpressibility  and  inactivity. 

Between  this  state  and  the  waking  state,  the  essential 
distinction  is  a  great  reduction  of  waste.  Certainly  in  some 
nervous  centres  and  probably  in  all,  waste  does  not  abso- 
lutely cease :  there  continue  those  emissions  of  force  which 
keep  up  the  vital  processes  ;  and  it  is,  I  think,  unlikely  that 
there  is  ever  an  entire  stoppage  of  those  changes  which  take 
place  in  the  highest  centres.  But  the  rate  of  waste  falls  so 
low  that  the  rate  of  repair  exceeds  it.  It  is  not  that  during 
the  period  of  activity  waste  goes  on  without  repair,  while 
during  the  period  of  inactivity  repair  goes  on  without  waste  ; 
for  the  two  always  go  on  together.  Very  possibly — probably 
even — repair  is  as  rapid  during  the  day  as  during  the  night : 
perhaps  even  more  rapid ;  for  the  blood  is  on  the  average 
richer  and  circulates  faster.  But  during  the  day  the  loss  is 
greater  than  the  gain,  whereas  during  the  night  the  gain  is 
diminished  by  scarcely  any  loss.  Hence  results  accumula- 
tion :  there  is  a  restoration  of  the  nerve-tissue  to  its  state  of 
integrity. 

In  the  course  of  some  hours  this  restoration  begins  to 


90  THE    DATA   OF   rSYCHOLOGT. 

show  its  effects  in  rctui-ning  impressibility.  While  in 
sleepiness  we  see  a  decreasing  readiness  to  respond  to  ex- 
ternal stimuli,  the  approach  to  a  waking  state  is  character, 
ized  by  an  increasing  readiness  to  respond  to  external  stimuli. 
Throughout  the  period  of  quiescence  the  afferent  nerves 
remain  subject  to  incident  forces.  The  pressure  of  the  body 
on  the  bed  affects  some  of  them,  and  others  are  affected  by 
the  touch  of  the  bed-clothes  ;  degrees  of  heat  a  little  above 
or  below  the  average,  act  on  others  ;  and  yet  others  receive 
sonorous  vibrations  constantly  occurring.  But  whereas 
sleep  results  because  the  centres  worn  by  action  become 
less  and  less  sensitive  to  these  stimuli,  waking  results 
because  the  centres  repaired  during  rest  become  more  and 
more  sensitive  to  them.  The  strains  of  muscles  and  liga- 
ments which  during  the  first  part  of  the  night  fail  to  cause 
changes  of  attitude,  cause  such  changes  towards  morn- 
ing. The  amount  of  light  that  traverses  the  eye-lids  pre- 
sently suffices  to  call  forth  movements.  Some  slight  noise 
which,  hours  before,  would  have  had  no  effect,  now  produces 
a  start.  Even  in  the  absence  of  external  stimuli  (which, 
however,  can  never  be  absent)  there  are  the  stimuli  from  the 
viscera,  and  especially  from  the  alimentary  canal :  an  empty 
stomach  eventually  sends  to  the  cerebro-spinal  system 
enough  disturbance  to  end  the  quiescent  state.  The  longer 
repair  goes  on  unopposed  by  appreciable  waste,  the  greater 
must  become  the  instability  of  the  nerve-centres,  and  the 
greater  their  readiness  to  act ;  so  that  there  must  at  length 
come  a  time  when  the  slightest  impressions  will  produce 
motions.  Such  impressions,  however  slight,  are  necessary 
antecedents.  There-integrated  nerve-centres  do  not  resume 
their  activity  until  an  impulse  arriving  from  the  periphery 
overthrows  some  of  their  molecules.  Evidence  of  this  is 
furnished  to  most  every  morning.  On  awakening  from 
refreshing  sleep,  there  commonly  occurs  an  involuntary 
stretching  of  the  muscles  of  the  whole  body ;  showing  an 
immense  undirected  motor  discharge.     But  this  is  not  the 


NERVOUS    STIMULATION   AND   NERVOUS    DISCHARGE.  91 

initial  fact.  No  one  awakes  to  find  himself  then  and  there 
stretching;  which  might  happen  were  the  discharge  spon- 
taneous. It  comes  after  those  stronger  disturbances  that 
are  propagated  to  the  centres^  as  soon  as  some  slight  distur- 
bance has  led  to  the  slight  movements  that  accompany 
waking.  A  trifling  sound  causes  opening  of  the  eyes  and 
a  turn  of  the  head.  Thereupon  follow  vivid  impressions 
through  the  eyes^  through  the  skin  that  rubs  against  tho 
bed-clothes,  and  through  the  muscles  that  set  up  the 
movements.  And  a  relatively-large  aggregate  of  stimuli 
being  sent  from  the  periphery,  there  results  this  relatively 
large  gush  of  motor  excitement. 

On  pursuing  the  argument  we  may  understand  why  the 
energies  continue  to  rise  for  some  time  after  awaking. 
We  saw  that  when  once  sleepiness  has  commenced,  it 
increases  because  in  proportion  as  the  nervous  centres  fail 
in  their  discharges,  the  heart,  losing  part  of  its  stimulus, 
begins  to  flag,  and  that  the  flagging  of  the  heart  leads  to  a 
greater  inertness  of  the  nerve-centres,  which  re-acts  as 
before.  Conversely,  it  will  here  be  manifest  that  when  the 
nerve-centres,  repaired  by  sleep,  become  again  ready  for 
discharging  with  vigour,  there  take  place  an  action  and  re- 
action which  have  the  opposite  effect.  The  pulsations  on  awak- 
ing are  comparatively  feeble.  As  soon  as  stimuli  begin  to  be 
received  through  the  sensory  organs,  and  the  discharges  of 
the  nerve-centres  are  renewed,  the  heart  comes  in  for  its  share 
of  these  and  acts  more  vigorously.  By  so  doing  it  supplies 
the  nerve-centres  with  more  blood  in  quicker  gushes.  A 
greater  nervous  discharge  is  thereby  made  possible,  which 
again,  among  other  results,  exalts  the  heart's  action.  And 
so  the  mutual  aid  goes  on :  the  greatest  nervous  vigour 
being  reached  when  the  vascular  activity  has  been  still 
further  raised  by  a  meal,  and  the  blood  has  been  enriched 
by  the  absorbed  materials. 

§  38.  As  implied  by  much  that  has  gone  before,  and  as 


92  THE    DATA   OF   PSYCHOLOGY, 

especially  implied  by  the  last  section,  nervous  stimulation 
and  nervous  discharge  have  always  both  special  and  general 
results.  Beyond  the  priuiary  and  definite  effect  wrought  on 
a  particular  part  by  a  particular  impression,  there  are  in 
every  case  secondary  and  indefinite  effects  diffused  through  the 
whole  nervous  system,  and  by  it  through  the  body  at  large. 
It  was  pointed  out  (§§  10, 11)  that  the  simplest  nerve-centre 
puts  in  relation  not  afferent  and  efferent  fibres  alone ;  but 
that  through  other  fibres,  commissural  and  centripetal,  con- 
nections are  made  between  it  and  other  nerve-centres  of  the 
same  grade  and  of  a  higher  grade.  Further,  we  saw  that 
when  such  a  nerve-centre  is  excited  through  an  afferent 
nerve,  the  disengaged  molecular  motion  does  not  escape 
wholly  along  one  or  more  efferent  nerves ;  but  that  part  of 
it,  propagated  to  higher  centres,  there  sets  vip  suppletuen- 
tary  changes.  The  diffusion  does  not  stop  here — remoter 
parts  are  reached;  and  thus  the  disturbance  of  a  single 
nerve-fibre,  if  at  all  considerable,  reverberates  throughout 
the  entire  nervous  system,  and  affects  all  the  functions  con- 
trolled by  it.  Digging  a  pin  into  the  foot  may  cause  a  con- 
vulsive contraction  not  of  the  leg-muscles  only,  but  of 
many  other  muscles  throughout  the  body.  At  the  same 
time  it  may  alter  the  rate  of  pulsation,  and  send  Avaves  of 
constriction  along  the  arteries.  The  excreting  structures 
of  the  skin  may  be  so  affected  that  a  burst  of  perspiration 
results ;  and  the  actions  going  on  throughout  the  alimentary 
canal  may  be  deranged.  Such  reverberations,  which  become 
conspicuous  when  the  disturbances  are  decided,  take  place 
also  when  they  are  slight.  A  more  vivid  light,  causing 
as  it  does  stronger  j)ulses  of  change  through  the  optic  nerve, 
increases  the  rate  of  respii'ation ;  and  doubtless  the  other 
vital  functions  are  simultaneously  exalted.  So  that  each 
nervous  impression,  beyond  a  direct  response  in  the  shape 
of  increased  action  from  one  or  more  organs,  calls  forth  an 
indirect  response  in  the  shape  of  increased  action  of  the 
organism  as  a  whole. 


NERVOUS    STIMULATION   AND   NERVOUS    JTOjHARtM 

Remembering  that  every  instant  tlie  disturbance  tbus 
eclioing  througliout  all  passages  of  the  nervous  system  is 
not  solitary^  but  that  there  are  many  such  disturbances,  here 
arising  from  pressure  there  from  touch,  in  this  place  pro- 
duced by  sound  and  in  that  by  light,  at  one  part  by 
muscular  strain  and  at  another  by  heat  or  cold ;  it  will  be 
manifest  that,  besides  the  few  distinct  Avaves  of  nervous 
change  working  their  distinct  effects,  there  are  multitudinous 
indistinct  waves,  secondary  and  tertiary,  travelling  in  all 
directions  working  their  indistinct  effects. 

§  39.  Since  such  reflected  and  re-reflected  disturbances 
everywhere  act  as  stimuli,  we  must  regard  the  entire 
nervous  system  as  at  all  times  discharging  itself.  The 
unstable  molecules  of  its  centres,  exposed  to  this  confused 
reverberation,  are  liable  to  be  decomposed  wherever  a 
concurrence  of  small  waves  makes  the  local  agitation  con- 
siderable ;  and  the  molecular  motion  thereupon  disengaged, 
adds  to  the  centrifugal  gush  perpetually  going  on.  Rightly 
to  conceive  nervous  action  then,  we  must  think  of  the  con- 
spicuous emissions  of  force  from  parts  of  the  nervous 
system  that  are  strongly  disturbed,  as  standing  out  from 
a  vague  back-ground  of  inconspicuous  emissions  from  the 
whole  nervous  system,  which  is  slightly  disturbed. 

To  this  general  nervous  disturbance  with  its  consequent 
general  discharge,  is  probably  due  a  certain  general  action 
of  the  motor  organs.  No  muscles  are  ever  in  a  state  of 
absolute  rest.  What  we  distinguish  as  muscular  motion 
is  produced  by  the  greater  contraction  of  some  muscles  than 
of  others.  The  others,  however,  are  all  slightly  contracted; 
and  would  severally  produce  motion  were  they  not  balanced 
or  out-balanced  by  their  antagonist  muscles.  This  per- 
vading activity  of  the  muscles  is  called  their  tonic  state. 
And  while  we  regard  particular  contractions  as  the  results 
of  particular  nervous  discharges,  we  have  good  reasons  for 
concluding  that    this   universal    contraction  is  the  result 


94  THE    DATA   OF   PSYCHOLOGY. 

of  the  universal  nervous  discliarge.  Here  are  a  few  of 
them.  Sleep,  as  above  explained,  implies  dimi- 

nislied  nervous  discLiarg-e,  special  and  general.  A  dimi- 
nution of  tlie  general  discharge  ought,  then,  to  be  shown 
in  a  decrease  of  the  tonic  contraction.  It  is  so  shown. 
Falling  asleep  is  accompanied  by  muscular  relaxation : 
though  previously  the  attitude  was  such  that  no  effort 
seemed  requisite  to  maintain  it  ;  yet  that  there  was 
some  muscular  strain,  and  that  it  has  suddenly  become 
less,  is  proved  by  the  sliding  down  of  a  limb,  or  of 
the  head,  to  a  more  stable  position.  Certain  dis- 

orders, as  palsy,  yield  further  proof.  The  flexors  and 
extensors  which,  when  duly  contracted,  serve  by  their 
balanced  antagonism  to  hold  a  limb  steady,  cease  to  do  this 
when  the  general  nervous  discharge  is  not  great  enough  to 
keep  them  and  all  other  muscles  braced  up :  in  default  of 
sufficient  stimulus  for  both,  now  one  set  and  now  the  other 
fails  to  put  the  due  check  on  its  opponent.  That  such 
shakings  are  so  caused,  we  see  clearly  in  persons  debilitated 
by  over- stimulation ;  for  in  them  this  symptom  may  be 
temporarily  mitigated,  or  almost  cured,  by  temporarily  in- 
creasing the  general  nervous  discharge.  The  drunkard  who 
eai-ly  in  the  day  cannot  lift  his  glass  without  spilling  the 
contents,  is  able  to  do  this  after  his  brain  has  been  excited 
by  the  usual  doses  of  alcohol. 

Of  course  it  is  not  the  muscles  alone  on  which  this  con- 
tinuous centrifugal  gush  is  expended.  Through  the  inter- 
mediation of  nerves  connecting  the  cerebro-spinal  system 
with  the  sympathetic  sj^stem,  the  viscera  receive  their  share 
of  it.  Hence  the  overflow  of  nervous  energy  which,  without 
special  solicitations,  diffuses  itself  throughout  the  motor 
structures,  giving  elasticity  to  the  step,  and  producing  the 
concave  bend  of  the  back,  the  opened-out  shoulders,  the 
raised  head,  &c.,  has,  for  its  simultaneous  results,  an 
accelerated  circulation,  an  invigorated  digestion,  and  an 
exaltation  of  the  vital  processes  at  large. 


NEUYOUS    STIMULATION   AND   NERVOUS   DISCHARGE.  95 

§  40.  Briefly  reviewed  from  a  somewliat  different  stand- 
point, the  following  are  the  leading  facts  which  it  concerns 
us  to  remember. 

Nervous  stimulations  and  discharges  consist  of  waves  of 
molecular  change,  that  chase  one  another  rapidly  through 
nerve-fibres.  The  stimulus  or  discharge  formed  of  such 
waves,  arises  at  some  place  where  unstable  nerve-substance 
has  been  disturbed ;  and  is  the  same  no  matter  what  agent 
caused  the  disturbance.  The  successive  waves  severally 
travel  with  a  velocity  which,  though  considerable  compared 
with  ordinary  sensible  motions,  is  extremely  slow  compared 
with  other  kinds  of  transmitted  molecular  motions.  And  each 
set  of  waves,  while  itself  caused  by  the  decomposition  of 
unstable  nerve-matter,  is  a  means  of  decomposing  other 
unstable  nerve-matter  :  so  generating  further  and  often 
stronger  sets  of  waves,  which  similarly  chase  one  another 
into  many  and  distant  parts  of  the  nervous  system. 

There  is  a  triple  rhythm  in  these  nervous  stimulations 
and  discharges-r— each  form  of  rhythm  being  due  to  the  greater 
or  less  incapacity  for  action  which  an  action  produces.  We 
have  seen  that  every  wave  of  isomeric  transformation  passing 
along  a  nerve-fibre,  entails  on  it  a  momentary  unfitness  to 
convey  another  wave;  and  that  it  recovers  its  fitness  only 
when  its  lost  molecular  motion  has  been  replaced  and  its 
unstable  state  thus  restored.  We  have  also  seen  that  any 
portion  of  grey  matter  in  a  nerve-centre,  which  having  been 
disturbed  and  partially  decomposed  has  emitted  a  shock  of 
molecular  change,  is  proportionately  incapacitated ;  and  that 
it  recovers  its  original  ability  only  as  fast  as  it  re-integrates 
itself  from  the  materials  brought  by  the  blood.  And  then 
there  comes  the  further  rhythm  constituted  by  the  alterna- 
tions of  sleep  and  waking — a  rhythm  having  the  same  origin 
r.s  the  last,  and  being  supplementary  to  it. 

The  remaining  truth  which  we  have  contemplated  is  that 
each  special  stimulation  and  the  special  discharge  produced 
by  it,  do  not  together  form  the  whole  of  every  nervous  act ; 


06  THE    DATA   OP   PSYCHOLOGY. 

but  tliat  there  is  always  an  accompanying  general  stimula- 
tion and  general  discharge.  Every  part  of  the  nei'vous 
system  is  every  instant  traversed  by  waves  of  mole- 
cular change — here  strong  and  here  feeble.  There  is  a 
universal  reverberation  of  secondary  waves  induced  by 
the  stronger  primary  waves,  now  arising  in  this  place  and 
now  in  that ;  and  each  nervous  act  thus  helps  to  excite  the 
general  vital  processes  while  it  achieves  some  particular 
vital  process.  The  recognition  of  this  fact  discloses  a  much 
closer  kinship  between  the  functions  of  the  nervous  system 
and  the  organic  functions  at  large,  than  appears  on  the  sur- 
face. Though  unlike  the  pulses  of  the  blood  in  many 
respects,  these  pulses  of  molecular  motion  are  like  them 
in  being  perpetually  generated  and  diffused  throughout  the 
body ;  and  they  are  also  like  them  in  this,  that  the  cen- 
tripetal waves  are  comparatively  feeble  while  the  centrifugal 
waves  are  comparatively  strong.  To  which  analogies  must 
be  added  the  no  less  striking  one,  that  the  performance  of 
its  office  by  every  part  of  the  body,  down  even  to  the 
smallest,  just  as  much  depends  on  the  local  gushes  of 
nervous  energy  as  it  depends  on  the  local  gushes  of  blood. 


X 


CHAPTER    YI. 

-ffiSTHO-PHYSIOLOGY.*  ^ 

§  41.  Throughout  the  foregoing  chapters  nervous  pheno- 
mena have  been  formulated  in  terms  of  Matter  and  Motion. 
If  from  time  to  time  the  phrases  used  have  tacitly  referred 
to  another  aspect  of  nervous  phenomena^  the  tacit  references 
have  formed  no  parts  of  the  propositions  set  down ;  but  have 

*  This  new  word  will  possibly  be  condemned  as  not  legitimately  com- 
pounded. The  objection  that  the  root  from  which  its  prefix  is  derived,  is 
shorn  of  its  fair  proportions,  admits,  I  am  told,  of  a  satisfactory  answer  : 
from  the  proximate  root,  appeal  may  be  made  to  the  original  root,  which, 
following  the  Greek  method  of  forming  derivatives,  would  admit  of  the 
required  modification.  But  to  the  criticism  that  the  word  involves  the 
logical  inconsistency  of  uniting  a  verb  with  a  noun,  there  is  no  such  suffi- 
cient answer.  Nevertheless,  I  deliberately  adopt  jEstho -physiology  in  pre- 
ference to  the  more  cumbrous  and  cacophonous  yEsthesi-physiology.  A 
progressive  integration  by  which  the  originally-distinct  and  numerous  parts 
of  compound  words  become  fused  together,  blurred,  and  some  of  them  lost, 
is  one  of  the  essential  processes  in  the  development  of  language.  If  man- 
kind had  refrained  from  the  obliteration  and  disfigurement  of  roots,  and 
parts  of  roots,  language  would  have  continued  wholly  inadequate  for  all  but 
its  simplest  functions.  Omitting  those  formed  by  onomatopoeia,  the  best 
words  are  those  from  which  long  use  has  worn  away  all,  or  nearly  all,  traces 
of  their  origin.  We  may  as  well,  therefore,  begin  with  abbreviated  and 
modified  words  when  we  have  to  coin  them  ;  instead  of  leaving  time  to 
bring  about  the  needful  shortening  and  shaping.  Those  who,  dealing  with 
words  as  counters,  see  that  their  convenience  as  counters  is  the  chief  con- 
sideration, will  probably  coincide  in  this  view  ;  though  I  suppose  it  will 
be  whoUy  disapproved  by  those  who  regard  words  not  as  counters  but  as 
money, 

7 


98  THE    DATA   OF   PSYCHOLOGY. 

been  due  to  lack  of  fit  words — words  free  from  unfit  associa-  ' 
tions.  As  already  said,  the  nervous  system  can  be  known 
only  as  a  structure  that  undergoes  and  initiates  either 
visible  changes,  or  changes  that  are  representable  in  terms 
furnished  by  the  visible  world.  And  thus  far  we  have 
limited  ourselves  to  generalizing  the  phenomena  which  it 
thus  presents  to  us  objectively. 

Now,  however,  we  turn  to  a  totally-distinct  aspect  of  our 
subject.  There  lies  before  us  a  class  of  facts  absolutely 
without  any  perceptible  or  conceivable  community  of  nature 
with  the  facts  that  have  occupied  us.  The  truths  here  to  be 
set  down  are  truths  of  which  the  very  elements  are  unknown 
to  physical  science.  Objective  observation  and  analysis  fail 
us ;  and  subjective  observation  and  analysis  must  supple- 
ment them. 

In  other  words,  we  have  to  treat  of  nervous  phenomena 
as  phenomena  of  consciousness.  The  changes  which,  re- 
garded as  modes  of  the  Non-Ego,  have  been  expressed  in 
terms  of  motion,  have  now,  regarded  as  modes  of  the  Ego, 
to  be  expressed  in  terms  of  feeling.  Having  contemplated 
these  changes  on  their  outsides,  we  have  to  contemplate 
them  from  their  insides.  To  speak  with  exactness,  indeed, 
it  cannot  be  said  that  ive  have  so  to  contemplate  these 
changes ;  for  this  expression  implies  that  these  changes  can 
be  simultaneous  witnessed  by  more  than  one,  which  is  not 
true.  Rigorously  limiting  the  proposition  to  that  which  is 
alone  possible,  it  amounts  to  this  : — I  have  to  describe  the 
laws  of  relation  between  the  states  of  feeling  occurring  in 
my  own  consciousness,  and  the  physical  afiections  of  that 
nervous  system  which  I  conclude  I  possess ;  and  the  reader 
has  to  observe  whether  in  himself  there  exist  parallel  rela- 
tions between  such  known  states  of  consciousness  and  such 
supposed  nervous  afiections. 

This  will  perhaps  be  thought  a  needlessly  roundabout,  if 
not  a  sceptical,  statement ;  but  it  is  in  fact  not  roundabout 
enough.     It  does  not  bring  sufficiently  into  view  the  re- 


^STHO-PHYSIOLOGY.  99 

motely-inferential  character  of  tlie  belief  that  feeling  and 
nervous  action  are  correlated.  Before  proceeding  on  tins 
belief,  let  us  observe  bow  indirect  is  the  path  wbicb  leads  to 
it. — 1.  Eacli  individual  is  absolutely  incapable  of  knowing 
any  feelings  but  his  own.  That  there  exist  other  sensations 
and  emotions,  is  a  conclusion  implying,  in  the  first  place, 
the  reasonings  through  wdiich  he  identifies  certain  objects 
as  bodies  of  like  nature  with  his  own  body ;  and  implying, 
in  the  second  place,  the  further  reasonings  which  convince 
him  that  along  with  the  external  actions  of  these  bodies, 
there  go  internal  states  of  consciousness  like  those  accom- 
panying such  external  actions  of  his  own  body.  2.  This 
conclusion  that  there  exist  beings  like  himself,  and  that 
under  like  conditions  they  experience  like  feelings,  even 
supposing  it  entirely  true  (and  it  is  not  entirely  true,  for 
many  facts  unite  to  prove  that  under  like  conditions  both 
the  quantities  and  the  qualities  of  sensations  and  emotions 
in  diSerent  individuals  diSer  considerably),  by  no  means 
implies  that  what  he  knows  under  its  subjective  aspect 
as  feeling,  is,  under  its  objective  aspect,  nervous  action. 
The  average  observer  has  no  direct  evidence  that  these 
other  like  beings  have  nervous  systems,  any  more  than  that 
he  has  himself  a  nervous  system;  and  he  has  no  direct 
evidence  in  the  one  case  any  more  than  in  the  other,  that 
nervous  excitations  are  the  causes  of  feelings.  Experi- 
mental physiologists  and  pathologists  only  have  proofs ;  and 
even  their  proofs  are  mostly  indirect.  The  experiments 
"which  yield  them  are  usually  made  on  beings  of  another  and 
much  inferior  order.  The  contractions  of  muscles  and 
arteries,  caused  by  irritating  nerve-trunks  in  frogs,  the 
convulsive  movements,  and  sometimes  the  sounds,  made  by 
birds  and  mammals  whose  nerve-centres  are  variously  in- 
jured— these  are  the  phenomena  from  which  it  is  inferred  that 
the  human  nervous  system  is  the  seat  of  the  human  feelings, 
and  that  these  feelings  are  the  correlatives  of  its  excitations : 
the  only  important  verifications  of  the  inference  being  those 


100  THE    DATA   OF    PSYCHOLOGY. 

obtained  during  surgical  operations  wliere  nerve-trunks  aro 
cut  through,  and  those  furnished  by  j^ost  mortem  examina- 
tions of  morbid  nervous  structures  in  the  bodies  of  those  who 
when  ahve  displayed  abnormal  excesses  or  defects  of  feel- 
ing. 3.  And  then,  having  learnt  at  second  hand,  through 
the  remotely-inferential  interpretation  of  verbal  signs,  that 
in  now  one  and  now  another  of  the  bodies  he  recognizes  as 
like  his  own  there  has  been  found  a  nervous  system,  and 
that  the  stimulations  of  this  produce  those  manifestations 
which  in  himself  accompany  feelings,  the  reader  imagines  a 
nervous  system  contained  in  his  own  body,  and  concludes 
that  his  sensations  and  emotions  are  due  to  the  disturbances 
which  the  outer  world  sets  up  at  its  periphery,  and  arouses 
by  indirect  processes  in  its  centres.  Such,  stated  as  briefly 
as  possible,  is  the  long  and  involved  series  of  steps  by  which 
alone  the  connection  between  nervous  action  and  feeling 
can  be  established. 

Nevertheless,  the  evidence  of  this  connection,  is  so  largo 
in  amount,  presents  such  a  congruity  under  so  great  a 
variety  of  circumstances,  and  is  so  continually  confirmed  by 
the  correct  anticipations  to  which  it  leads,  that  we  can 
entertain  nothing  more  than  a  theoretical  doubt  of  its  truth. 
Here  accepting  the  belief,  alike  popular  and  scientific,  that 
all  the  human  beings  known  objectively  have  feelings  like 
those  which  each  knows  subjectively ;  and  accepting  also 
the  belief,  originating  with  science  but  now  difiused  through 
the  general  mind,  that  feelings  are  the  concomitants  of 
nervous  changes ;  we  will  proceed  to  consider  the  relation 
between  feelings  and  nervous  changes  under  its  leading 
aspects. 

§  42.  And  first  let  us  observe  that  the  circumstances 
conducive  to  the  one  are  identical  with  the  circumstances 
conducive  to  the  other.  The  conditions  which  we  before 
found  essential  to  the  production  of  nervous  action,  we  shall 
now  find  essential  to  the  production  of  feeling.    We  may  pass 


-ESTHO-PHYSIOLOGY.  1 01 

over  the  evidences  briefly,  as  being  many  of  tbem  tlae  inner 
aspects  of  phenomena  already  observed  under  tbeir  outer 
aspects. 

That  without  continuity  of  nerve-fibre  between  periphery 
and  centre,  a  disturbance  at  the  one  causes  no  feehng  at  the 
other,  is  proved  to  every  one  who  has  cut  himself  deeply: 
for  a  long  time  the  part  that  has  had  its  nervous  com- 
munication destroyed,  remains  numb.  This  experience, 
usually  very  limited  in  each  person,  is  borne  out  by  the 
testimony  of  those  seriously  injured ;  and  especially  by  the 
testimony  of  those  whose  sensations  over  large  parts  of 
their  bodies  have  ceased,  and  who,  after  death,  are  found 
to  have  lesions  in  the  conducting  structures  of  the  nervous 
centres. 

The  hindrance  or  prevention  of  feeling  by  pressure,  is 
illustrated  by  the  numbness  of  a  limb  so  placed  that  its 
whole  weight,  and  perhaps  the  weight  of  another  limb 
lying  over  it,  comes  on  the  edge  say  of  a  table;  so  that 
great  stress  is  borne  by  some  portion  of  the  chief  nerve- 
trunk.  Local  ana3sthesia  thus  caused  in  strong  persons, 
is  caused  still  more  readily  in  feeble  persons ;  who,  on 
awaking,  not  unfrequently  find  complete  insensibility  of  the 
parts  that  have  been  pressed  against  the  bed  during  sleep. 

Ability  to  feel  depends  on  the  maintenance  of  a  certain 
temperature.  This  also  is  a  general  truth  of  which  some 
proof  is  furnished  to  every  individual  by  his  own  experience 
— or,  at  any  rate,  to  every  individual  inhabiting  a  climate 
where  the  Avinter's  frost  suffices  greatly  to  chill  the  ex- 
tremities. Evidence  much  stronger  but  indirect,  is  given 
him  by  those  who  have  undergone  surgical  operations  in 
parts  deprived  of  feeling  by  freezing  mixtures  or  by  ether- 
spray.  Loss  of  local  sensibility  from  local  cold,  ordinarily 
not  very  manifest  unless  the  cold  is  great,  becomes  manifest 
when  the  cold  is  slight  if  the  circumstances  supply  a  delicate 
test.  This  is  interestingly  shown  among  compositors.  The 
air  of  a  printing-office  has  to  bo  kept  very  warm,  even  at 


102  THE    DATA   OF   PSYCHOLOGY. 

the  expense  of  unlicaltliy  closeness ;   otlierwise  the  fingers . 
of  the  compositors   cease  to  lay  hold  of,  and  manipulate, 
the  types  with  the  requisite  nicety  and  speed. 

Few  persons  have  immediate  experience  of  the  fact  that 
defect  of  blood  in  a  part  causes  defective  sensibility  of  that 
part ;  but  all  persons  have  immediate  experience  of  the 
local  exaltation  of  sensibility  that  accompanies  local  excess 
of  blood.  The  inflamed  neighbourhood  of  a  wound,  or 
even  the  surface  of  a  pimple,  yields  to  consciousness  when 
touched,  an  amount  of  feeling  far  greater  than  is  yielded  by 
a  part  of  the  skin  supplied  with  the  ordinary  amount  of 
blood.  Special  organs  of  touch  show  us  well  the  increased 
sensitiveness  thus  caused.  When  one  of  those  sacs  con- 
taining the  bulbs  of  the  small  hairs  scattered  over  the  skin, 
is  congested,  the  rubbing  of  the  clothes  against  the  hair 
growing  from  it,  especially  if  it  has  been  broken  short,  pro- 
duces an  unbearable  smart.  Among  evidences  yielded  by 
the  other  senses,  a  familiar  one  is  the  intolerance  of  hght 
that  goes  along  with  inflammation  of  the  eyes.  And  there 
is  an  unfamiliar  one  particularly  worth  noting,  because 
it  exhibits  the  effect  due  to  increased  quantity  of  blood 
apart  from  increased  temperature.  The  observation  may 
be  made  when  taking  a  hot  bath.  Let  the  water  be  above 
blood-heat — say  100°  Fh.  After  remaining  quiet  for  a  time 
until  equally  heated  all  over,  stand  up  and  rub  one  portion 
of  the  body  with  a  fiesh-brush  until  it  is  red.  Pause 
a  few  moments,  and  lie  down  again  in  the  water.  It  will 
then  be  perceived  that  to  the  reddened  part  the  water  seems 
much  hotter  than  it  does  to  any  other  part.* 

That  degree  of  feeling  is  affected  by  quality  of  blood  as 
well  as  by  quantity,  is  a  truth  not  easily  discerned  within  the 

*  This  fact  yields  proof,  if  there  needs  any,  that  the  nerves  which 
appreciate  temperature  are  not  the  nerves  of  touch.  Violent  friction  must 
produce  a  momentary  incapacity  of  the  nerves  of  touch  ;  and  this  in- 
capacity would  be  shown  in  a  decreased,  instead  of  an  increased,  appreciation 
of  temperature,  were  they  the  agents  concerned. 


^STHO-FHYSIOLOGY.  103 

expeiiences  of  eacli  individual^  if  attention  is  limited  to  those 
variations  of  feeling  that  accompany  naturally -produced 
variations  in  quality  of  blood.  For  such  variations  cannot 
be  identified  with  precision ;  and  they  arise  so  slowly  that  the 
concomitant  mental  states  cannot  be  brought  into  close  con- 
tiguity, so  as  to  bring  out  their  contrasts  clearly.  But  by 
making  certain  artificial  additions  to  the  blood,  every  one 
gets  proof  of  the  connection  between  its  quality  and  the 
genesis  of  feeling.  The  effects  of  stimulants  on  conscious- 
ness are  mostly  traced  in  the  intensification  of  those  in- 
ternally-initiated feelings  with  which  we  shall  deal  pre- 
sently; but  they  may  also  sometimes  be  traced  in  the 
intensification  of  the  externally  -  initiated  feelings.  In 
nervous  subjects,  ordinary  impressions  on  the  senses 
are  often  rendered  abnormally  acute  by  tonics.  When 
under  the  influence  of  opium,  music  that  was  previously 
unenjoyed  may  be  greatly  enjoyed ;  and  it  is  a  well-known 
result  of  hashish  to  give  an  excessive  vividness  to  the 
sensations. 

How,  contrariwise,  there  are  substances  which,  when 
added  to  the  blood,  render  sentiency  less  vivid,  is  shown 
by  other  facts  similarly  reached.  We  have  sedative 
medicines — medicines  that  diminish  the  amounts  of  painful 
consciousness  caused  by  irritations  at  the  periphery  of 
the  nervous  system.  And  we  have  agents  of  the  same 
class  called  anassthetics,  which,  in  a  still  greater  degree, 
hinder  the  genesis  of  feelings  by  the  actions  that  usu- 
ally generate  them.  These  efiects  so  caused,  help  us  to 
understand  the  stupor  produced  by  the  natural  anesthetics, 
carbonic  acid  and  urea;  and  prove  that  some  variations 
in  degree  of  feeling  are  determined  by  variations  in  the 
activities  of  excreting  organs. 

§  43.  Now  that  we  have  noted  how  feelings  and  nervous 
changes  are  facilitated  or  hindered  by  the  same  conditions,  we 
may  go  on  to  collate  them  in  detail.     Let  us  begin  by  distin- 


104  THE    DATA   OP   PSYCHOLOGY. 

guishing  those  nervous  cTianges  wliich.  are  accompanied  by 
feelings  from  those  which  are  not.  For,  as  we  noted  in 
passing,  several  classes  of  them  have  objective  aspects  only 
— do  not  present  inner  faces  to  consciousness ;  and  others 
have  subjective  aspects  in  early  life  but  cease  to  have  them 
in  adult  life. 

Chief  among  the  nervous  changes  that  have  no  identifi- 
able subjective  aspects,  are  those  occurring  in  the  visceral 
nervous  system.  So  long  as  they  are  normal  in  their 
amounts,  the  stimulations  and  discharges  of  which  the 
sympathetic  is  the  seat,  go  on  without  sensations ;  and  even 
when  abnormal,  the  resulting  discomfort  or  pain  is  probably 
not  due  to  them  but  to  disturbance  of  those  cerebro-spinal 
fibres  whichaccompany  the  sympathetic  through  all  its  branch- 
ings. Similarly  with  the  local  ganglia  and  fibres  of  the  heart. 
Ordinai-ily  there  is  no  consciousness  of  the  heart's  action ; 
and  even  when  the  pulsations  are  violent,  the  modifications 
of  consciousness"  do  not  arise  from  the  state  of  the  heart's 
nervous  system,  but  from  disturbance  of  cerebro-spinal 
nerves  caused  by  the  bounds  of  the  heart  against  adjacent 
structures.  The  like  holds  with  the  vaso-motor  nerves. 
Under  ordinary  conditions  these  regulate  the  diameters  of 
the  arteries  without  our  knowing  anything  about  it;  and 
though  where,  as  in  a  blush,  great  dilatation  of  the  vessels 
has  been  produced,  we  are  made  aware  of  their  action,  yet 
we  are  made  aware  of  it  indirectly,  through  the  local  change 
in  the  quantity  of  blood  and  the  consequent  effect  on  the 
nerves  that  appreciate  temperature. 

The  majority  of  stimulations  and  discharges  occurring  in 
the  spinal  cord,  have  subjective  accompaniments.  These, 
however,  are  not  localized  at  those  points  in  the  spinal  cord 
where  the  essential  nervous  changes  take  place ;  as  is 
proved  by  the  fact  that  when  some  lesion  of  the  spinal 
cord  which  has  not  injured  its  lower  part,  has  cut  ofi"  com- 
munication with  the  brain,  the  reflex  acts  performed  by  this 
lower  part  are  unconscious.     Proceeding  upon  the  inference 


^STHO-PHYSIOLOGY.  105 

before  drawn  (§21)  tliat  wHen  a  wave  of  disturbance 
brouglit  by  an  afferent  nerve  to  a  spinal  centre,  liberates  a 
quantity  of  molecular  motion,  a  portion  of  it,  not  discharged 
along  the  efferent  nerves,  is  propagated  tbrougli  a  centri- 
petal nerve  to  a  higher  centre,  we  may  conclude  that  it  is 
this  portion  which  comes,  in  the  higher  centre,  to  have  a 
subjective  aspect  as  a  sensation  :  being  there  joined  with 
other  sensations  and  feelings  of  other  orders  into  a  chain 
of  states  of  consciousness,  out  of  which  no  sensation  is  ever 
known  to  exist.  For  recognition  of  a  sensation  as  such  or 
such,  necessitates  the  bringing  of  it  into  relation  with  the 
continuous  series  of  sentient  states,  from  some  of  which, 
simultaneously  experienced,  it  is  dissociated  by  perceived 
unlikeness,  and  with  others  of  which,  previously  ex- 
perienced, it  is  associated  by  perceived  likeness ;  and  the 
implied  comparisons  of  sentient  states  are  impossible  unless 
the  correlative  nervous  changes  are  put  in  connexion  at  one 
place.  It  does  not  follow,  as  it  at  first  seems  to 

do,  that  feelings  are  never  located  in  the  inferior  nervous 
centres.  On  the  contrary,  it  may  well  be  that  in  lower 
types  the  homologues  of  these  inferior  centres  are  the  seats 
of  consciousness.  The  true  implication  is  that  in  any  case 
the  seat  of  consciousness  is  that  nervous  centre  to  which, 
mediately  or  immediately,  the  most  heterogeneous  impres- 
sions are  brought ;  and  it  is  not  improbable  that  in  the 
course  of  nervous  evolution,  centres  that  were  once  the 
highest  are  supplanted  by  others  in  which  co-ordination  is 
carried  a  stage  further,  and  which  thereupon  become  the 
places  of  feeling,  while  the  centres  before  predominant 
become  automatic. 

Quite  congruous  with  this  conception  is  the  above-named 
fact,  that  certain  nervous  changes  which  have  subjective 
sides  early  in  life  cease  to  have  them  later  in  life.  Many 
acts  performed  by  the  child  slowly  and  consciously,  the 
adult  performs  rapidly  and  unconsciously.  Every  step 
taken  during  the  first  efforts  to  walk  has  its  accompanying 


106  THE    DATA   OP   PSYCHOLOGY. 

distinct  feelings  ;  but  eventually,  tlie  successive  »tep3  are 
made  wliile  consciousness  is  wliolly  or  almost  wholly  occu- 
pied witli  otlicr  feelings.  Still  better  is  tlie  illustration 
furnished  by  speecli.  Each  muscular  adjustment  of  tho 
vocal  organs  and  each  articulate  sound  made,  have,  in 
childhood,  concomitant  sentient  states  that  are  vivid,  and, 
for  the  moment,  all-absorbing.  Gradually,  however,  these  be- 
come less  dominant  in  consciousness ;  until  at  maturity  there 
is  entire  oblivion  of  the  one,  and  sometimes  partial  oblivion 
of  the  other :  witness  the  not  unfrequent  verbal  mistakes 
unconsciously  made  in  the  heat  of  discussion.  Now  facts  of 
this  kind,  countless  in  number  and  of  many  varieties, 
are  explicable  if  we  regard  feelings  as  the  subjective  sides  of 
such  nervous  changes  only,  as  are  brought  to  the  general 
centre  of  nervous  connections.  When  we  remember  that 
early  in  life  each  inferior  ganglion,  or  cluster  of  co- 
operating inferior  ganglia,  is  imperfectly  organized,  and  the 
connections  among  its  fibres  incomplete ;  we  shall  see  that 
if  there  comes  to  it  a  disturbance,  the  gush  of  molecular 
motion  liberated,  not  having  in  the  incompletely-connected 
commissural  and  efferent  fibres,  adequate  channels  of 
escape,  will  part  of  it  escape  along  a  centripetal  fibre  to 
a  higher  centre,  so  awakening  a  feeling.  And  it  will  mani- 
festly happen  that  the  approach  to  automatic  action  of  the 
lower  centre,  will  be  an  approach  to  a  state  in  which 
the  liberated  molecular  motion,  having  in  the  efferent  fibres 
fully-opened  channels  of  emission,  will  little  or  none  of 
it  be  forced  into  centripetal  fibres,  and  will  so  awaken  little 
or  no  feeling.  It  is  a  corollary  from  this  interpretation, 
that  all  gradations  will  exist  between  wholly  unconscious 
nervous  actions  and  wholly  conscious  ones ;  since  there  will 
bo  all  gradations  in  the  relative  amounts  of  the  disturb- 
ances which  take  their  courses  along  centripetal  fibres.  It 
obviously  follows,  too,  that  in  adult  life  a  nervous  action 
may  or  may  not  have  an  identifiable  subjective  aspect, 
according  as  it  is  strong  or  weak ;  since,   if  there    comes 


iRSTHO-PHYSIOLOGY.  107 

to  a  finislied  ganglion  constructed  as  described_,  a  feeble 
disturbance,  the  wliole  of  the  small  quantity  of  molecular 
motion  liberated  may  be  drafted  off  by  the  efferent  fibres ; 
whereas,  if  the  disturbance  is  great,  the  disengaged 
molecular  motion,  being  more  than  can  find  its  way  along 
the  efferent  fibres,  will  some  of  it  take  a  centrij^etal  course 
and  cause  a  subjective  change. 

§  44.  A  kindred  aspect  of  this  correlation  presents  itself 
when  we  contemplate  feeling  as  occupying  time.  A  sub- 
jective state  becomes  recognizable  as  such,  only  when  it  has 
an  appreciable  duration :  it  must  fill  some  space  in  the 
series  of  states,  otherwise  it  is  not  known  as  present.  This 
general  truth  harmonizes  with  a  general  truth  before 
pointed  out  respecting  nervous  action,  as  well  as  with  the 
above  interpretation. 

The  observed  fact  that  time  is  taken  in  the  transit  of  a 
nerve-wave,  is  not  to  the  point ;  for  this  transit  has  no 
concomitant  subjective  state.  But  the  inferred  fact  that 
the  change  set  up  in  a  nerve-centre  must  take  time,  and 
a  more  considerable  time  (§  35),  is  relevant ;  for  what  is 
objectively  a  change  in  a  superior  nerve-centre  is  subjectively 
a  feeling,  and  the  duration  of  it  under  the  one  aspect 
measures  the  duration  of  it  under  the  other. 

That  feeling  persists  after  the  force  arousing  it  ceases,  is 
not  proved  by  the  lengthened  sensation  produced  by  a 
moderate  blow  on  the  skin,  or  by  that  which  follows  dip- 
ping the  hand  into  hot-water,  or  by  those  which  the  palate 
and  the  nostrils  experience  from  pungent  substances  mo- 
mentarily applied ;  for  though  in  such  cases  the  external 
action  of  the  exciting  agency  is  brief,  the  local  changes  it 
sets  up,  lasting  some  time,  continue  for  some  time  to  dis- 
turb the  local  nerve-fibres.  But  good  evidence  is  supplied 
by  impressions  on  the  retina.  To  quote  the  words  of 
Professor  Huxley  : — "  A  flash  of  lightning  is,  practically, 
instantaneous,  but  the  sensation  of  light  produced  by  that 


108  THE    DATA   OP   PSYCHOLOaY. 

flash  endures  for  an  appreciable  period.  It  is  found,  in 
fact,  tliat  a  luminous  impression  lasts  for  about  one-eiglitli 
of  a  second;  wlience  it  follows,  that  if  any  two  luminous 
impressions  are  separated  by  a  less  interval,  they  are  not 
distinguished  from  one  another.  For  this  reason  a 
'  Catherine-wheel,*  or  a  lighted  stick  turned  round  very 
rapidly  by  the  hand,  appears  as  a  circle  of  fire ;  and  the 
spokes  of  a  coach- wheel  at  speed  are  not  separately  visible, 
but  only  appear  as  a  sort  of  opacity,  or  film,  within  the  tire 
of  the  wheel.'* 

As  above  said,  this  general  truth  that  feeling  implies 
time,  harmonizes  with  the  interpretation  given  in  the  pre- 
ceding section;  and  supplies  a  further  elucidation  of  the 
relation  between  conscious  and  unconscious  nervous  action. 
For  manifestly,  in  proportion  as  nervous  co-ordinations 
become  more  automatic  they  become  more  rapid;  and 
for  this  reason  also,  cease  to  present  such  conspicuous 
subjective  aspects.  Returning  to  the  inferior  ganglion, 
or  cluster  of  co-operating  ganglia,  above  described,  it 
will  be  obvious  that  a  state  in  which  the  local  or- 
ganization is  incomplete,  and  the  various  afferent  and 
commissural  fibres  not  brought  into  definite  relations  with 
vesicles,  and  through  them  with  efferent  fibres,  must  be 
a  state  in  which  the  molecular  motion  liberated  by  an  in- 
coming shock  of  change,  will  pass  through  the  imperfectly 
differentiated  structure  with  comparative  slowness  ;  and 
there  will  therefore  be  an  appreciable  time  during  which 
centi'ipetal  fibres  may  receive  disturbance.  But  as  fast  as 
the  local  connections  of  fibres  and  cells  become  complete, 
the  gush  of  molecular  motion,  following  the  completely- 
formed  channels,  wall  escape  rapidly ;  and  the  period  during 
which  excitement  of  the  centripetal  fibres  may  take  place 
will  be  abridged.  The  concomitant  subjective  state  will 
therefore  bo  rendered  shorter  by  the  same  change  that 
renders  it  feebler. 


X 


0*^  '['HI?  '^^^^ 


JCSTHO-PHYSIOLOGlSjs^^  ;  p q  tj  "^^       109 

§  45.  The  fact  that  each  feeling  lasts  an  appreciable  time, 
introduces  us  to  the  allied  fact  that  each  feeling  produces 
a  gi-eater  or  less  incapacity  for  a  similar  feeling,  which  also 
lasts  an  appreciable  time.  This,  too,  is  the  subjective  side 
of  a  phenomenon  before  noticed  under  its  objective  side 
(§  36).  For  as  the  duration  of  a  feeling  answers  to  the 
duration  of  the  molecular  disintegration  in  a  disturbed 
nerve-centre;  so  the  subsequent  interval  of  diminished 
ability  to  feel,  answers  to  the  interval  during  which  the 
disintegrated  nerve-centre  is  re-integrating  itself.  Let  us 
observe  how  among  sensations  of  all  kinds  we  may  trace 
conformity  to  this  law. 

An  illustration  is  supplied  by  the  sense  of  touch.  If  the 
fingers  be  repeatedly  swept  rapidly  over  something  covered 
by  numerous  small  prominences,  as  the  papillated  surface 
of  an  ordinary  counterpane,  a  peculiar  feeling  of  numbness 
in  them  results  :  the  objects  touched  the  moment  after  seem 
smoother  than  usual ;  implying  that  the  small  irregularities 
on   them    produce   less   vivid   impressions.  That 

the  sensation  of  muscular  tension  undergoes  a  variation 
similarly  caused,  everyone  knows.  After  carrying  a  very 
heavy  body  in  the  hand  for  some  time,  a  small  body  held 
in  the  same  hand  appears  to  have  lost  its  weight ;  showing 
that  the  nerve-centre  which  is  the  seat  of  the  sensation  has 
been,  for  the  moment,  rendered  obtuse.  How  the 

gustatory  faculty  is  exhausted  for  a  time  by  a  strong  taste, 
daily  experience  teaches.  When  sugar  or  honey  has  just 
been  eaten,  things  that  are  but  slightly  sweetened  seem  to 
have  no  sweetness.  While  the  palate  is  still  hot  with 
a  curry,  an  unflavourcd  dish  seems  insijDid ;  and  a 
glass  of  liqueur  is  fatal  to  the  appreciation  of  a  choice 
wine.  Even  more  marked  is  that  incapacity  of 

the  sense  of  smell  caused  in  like  manner.  The  intensity 
of  the  pleasurable  feeling  given  by  a  rose  held  to  the 
nostrils,  rapidly  diminishes  ;  and  when  the  sniffs  have  been 
continued  for  some  time,   scarcely  any  scent  can  be  per- 


110  THE  DATA  OP  PSYCHOLOaY 

ceived.  A  few  minutes^  rest  partially  restores  tlie  impressi- 
bility; but  a  long  interval  must  elapse  before  the  odoui' 
is  enjoyed  as  keenly  as  at  first.  This  quick  exhaustion, 
producing  in  such  cases  some  disappointment,  has  its 
correlative  advantage  "when  the  smells  are  disagreeable. 
Very  soon  these  become  much  less  perceptible ;  and  to 
those  living  in  it  a  stench  gives  scarcely  any  annoy- 
ance. The  feelings  generated  by  sonorous  vibra- 
tions rarely  show  us  this  variation  in  a  marked  degree; 
being,  as  they  commonly  are,  too  short  to  leave  much 
nervous  prostration.  A  strong  taste,  or  odour,  or  sensation 
of  muscular  tension,  is  due  to  an  action  on  the  nerves  that 
is  maintained  for  a  considerable  time ;  but  the  actions  to 
which  are  due  those  loud  sounds  required  to  cause  tempo- 
rary unimpressibility,  are  mostly  very  brief.  Illustrations 
are  to  be  expected  only  in  special  cases ;  and  in  these  we 
find  them.  The  bang  of  a  cannon  is  described  as  deafening* 
by  those  who  are  close  to  the  cannon  when  it  is  fired,  be- 
cause they  are  rendered  for  a  time  partially  deaf  to  ordi- 
nary sounds.  On  men  engaged  in  artillery-practice,  the 
repeated  explosions  entail  a  dulness  of  hearing  that  lasts 
for  hours  ;  and  this  dulness  of  hearing  becomes  per- 
manent in  those  who  are  permanently  occupied  in  such 
pi-actice.  Numerous  and  very  conclusive  proofs 
are  supplied  by  the  feelings  we  receive  from  light.  There 
are  two  classes  of  them  :  those  showing  us  a  variable  sensi- 
bility to  light  in  general,  as  contrasted  with  darkness ;  and 
those  showing  us  a  variable  sensibility  to  each  kind  of  light 
— each  colour.  Under  the  one  head  the  reader  may  first  bo 
reminded  of  the  experience  that  on  going  out  of  broad  sun- 
shine into  a  dimly-lighted  place,  it  is  impossible  to  discern 
the  surrounding  objects  :  only  after  a  time  do  they  become 
faintly  visible,  and  a  considerable  interval  elapses  before  they 
are  seen  with  clearness.  Disabilities  similarly  caused  are  dis- 
closed, when,  instead  of  acting  on  the  retinae  as  wholes,  we 
act  differently  on  their  different  parts.  Hence  what  are  called 


a:STHO-PHYSIOLOGY.  Ill 

negative  images.  If,  after  gazing  for  some  moments  at  an 
object  presenting  strong  contrasts  of  liglit  and  dark  parts, 
tlie  eyes  are  turned  towards  a  sliaded  space,  containing  no- 
thing conspicuous,  tliere  will  be  perceived  a  transient  image 
of  tlie  object,  in  wliicli  tlie  liglit  and  dark  parts  are  re- 
versed. Tlie  interpretation  of  tliis  fact  is  that  those  por- 
tions of  each  retina  on  which  strono-  lio-lit  had  fallen,  to- 
gether  with  the  answering  portions  of  the  optic  centres, 
having  -undergone  the  most  change  with  correspond- 
ing production  of  the  most  feeling,  are  the  next  in- 
stant less  capable  of  undergoing  change  and  evolving 
feeling  than  the  portions  on  which  feeble  light  had  fallen; 
and  hence,  when  they  are  together  exposed  to  the  same 
feeble  light,  the  unexhausted  parts  appreciate  it  more  than 
the  exhausted  parts,  and  a  negative  image  results.  The 
cases  of  the  second  class  are  the  well-known  phenomena  of 
subjective  complementary  colours.  After  looking  intently 
at  a  surface  of  bright  red,  an  adjacent  surface  of  white 
seems  to  have  a  greenish  tint.  The  explanation  is  obvious. 
Those  nervous  elements  changed  by  the  rays  which  produce 
in  us  the  sensation  of  redness,  having  been  partially  inca- 
pacitated, the  red  rays  contained  in  the  white  light  cause 
less  of  their  appropriate  effect  than  usual ;  while  the  blue 
and  yellow  rays  causing  their  usual  effects,  and  therefore 
relatively-predominant  effects,  a  sensation  of  greenness 
arises. 

This  decrease  in  the  susceptibility  to  a  feeling  of  any 
kind,  which  immediately  follows  a  feeling  of  that  kind, 
is  not  a  constant  decrease.  It  is  a  decrease  that  varies 
greatly  in  degree ;  and  from  its  variation  we  may  derive 
further  instructive  evidence.  Other  things  equal,  it  is  small 
or  great  according  to  the  great  or  small  constitutional 
vigour.  One  of  these  disabilities  lasts  for  a  scarcely 
appreciable  time  when  the  vital  activities  are  hio-h; 
and  lasts  for  a  time  that  becomes  longer  and  lono-er 
as    the   vital   activities    flag.     Abundant   proof  of  this   is 


112  THE-  daVa  op  psychology. 

furnislied  by  tlie  negative  images  just  described.  In 
youth  tliese  are  scarcely  if  at  all  to  be  observed :  only 
when  an  extremely-vivid  retinal  impression  lias  been  pro- 
duced, as  by  looking  at  tbe  Sun,  is  tbe  negative  image 
perceptible.  But  in  middle  life  and  afterwards,  especially 
in  debilitated  persons,  negative  images  of  ordinary  objects 
are  very  commonly  perceived,  and  often  bave  considerable 
durations.*  Feeling  being  tbe  subjective  correlate  of  tliat 
wliicb.  we  know  objectively  as  nervous  action,  tliese  facts 
are  obvious  corollaries  from  facts  set  down  in  tlie  last 
cliapter.  We  there  saw  that  the  excitement  of  a  nerve- 
centre  involves  waste ;  and  that  restoration  of  the  nerve- 
centre  to  a  state  of  equal  susceptibility  can  be  effected 
only  by  repair.  Hence  the  return  of  fitness  for  what  is 
objectively  stimulation  and  subjectively  feehng,  will  vary 
in  quickness  according  to  the  rate  of  repair.  When  the 
blood  is  rich  and  rapidly  circulated,  the  partial  disability 
will  be  but  momentary ;  and,  unless  the  sensation  has  been 
intense,  will  be  inappreciable.  But  along  with  failing  nutri- 
tion of  the  tissues,  the  disability  will  become  marked  and 
its  duration  longer.  In  further  illustration  of  this,  I  may 
name  the  fact  that  negative  images  are  most  conspicuous 
on  awaking  in  the  morning,  when  the  circulation  is 
slow.  The  sense  of  hearing  yields  parallel  evi- 

dence;   though  evidence  of  which  the  parallelism  is  not 

*  This  change  comes  on  so  gradually  that  very  few  remark  it  ;  and  the 
usual  supposition  is  that  negative  images  are  much  the  same  at  all  ages  and 
in  all  persons.  I  am  able,  however,  to  give  personal  testimony  to  the  con- 
trary. When  about  twenty  years  of  age,  my  attention  was  dra^vn  by  my 
father  to  a  case  in  which  the  circumstances  were  favourable  for  perceiving 
the  negative  image,  and  in  which  he  perceived  it  clearly.  To  me  it  was 
invisible  ;  and  I  well  remember  his  remark,  that  I  should  begin  to  see 
such  images  as  I  became  older.  He  was  right.  I  now  see  them  distinctly ; 
and,  moreover,  I  observe  that  they  are  most  distinct  at  times  of  least 
vigour.  It  is  worth  while  inquiring  how  far  this  change  affects  the 
appreciation  of  the  chromatic  harmonies.  It  seems  inferable  that  the 
harmonies  of  complementary  colours  become  more  perceptible  as  life  ad- 
vances. 


^STHO-PHYSre^te*'*'  U  '-l  LH  ^^^^       ^13 


immecliately  obvious.  Persons  on  whom  old  age  or  debility- 
brings  deafness^  frequently  describe  themselves  as  having 
no  difficulty  in  hearing  sounds^  but  as  being  unable  to 
disentagle  and  identify  words  when  they  are  indistinctly 
or  rapidly  uttered.  Supposing  that  in  such  cases  the 
nervous  structures  concerned  suffer  from  faulty  nutrition, 
we  have  an  explanation  of  this  peculiarity.  For  if  each  of 
the  successive  sounds  entails  waste  of  the  auditory  centres, 
and  leaves  them  less  sensitive  to  like  sounds,  it  must  fol- 
low that,  when  re-integration  is  slow,  the  like  sounds  im- 
mediately afterwards  received  will  produce  less  than  their 
due  amounts  of  sensation.  These  defects  of  sensation  will 
show  themselves  most  in  a  comparative  deadness  to  those 
delicate  consonantal  modifications  by  which  words  are 
mainly  distinguished  from  one  another — the  utterances 
listened  to  will  seem  a  series  of  vowel-sounds  joined  by 
blurred  consonants.  Hence  the  reason  why  persons  thus 
affected,  ask  those  who  address  them  to  articulate  slowly 
and  clearly.  The  confusion  of  impressions  produced  by 
rapid  speech  on  auditory  centres  thus  debilitated,  may  be 
conceived  by  supposing  debilitated  optic  centres  to  be 
similarly  treated.  If  a  person  in  whom  the  negative 
images  are  strong,  has  a  series  of  objects  passed  before 
his  eyes  so  fast  that  he  can  have  only  a  momentary  glance 
at  each  (to  parallel  the  momentary  opportunity  which  the 
cars  have  of  identifying  each  successive  articulation) ;  then 
it  will  manifestly  happen  that  the  negative  image  of  each 
object  will  interfere  with,  and  confuse,  the  positive  image 
of  the  next ;  and  such  a  person  will  therefore  not  identify 
the  successive  objects  so  readily  as  one  whose  optic  centres 
are  repaired  with  normal  speed.  As  confirming  the  be- 
lief that  this  defect  of  hearing  is  so  caused,  I  may  add 
that  it  frequently  co-exists  with  the  defect  of  vision  to 
which  I  have  compared  it ;  and  also  that  the  one,  like  the 
othei',  is  most  marked  early  in  the  day,  and  is  diminished 
by  whatever  invigorates  the  circulation. 


114  THE   DATA   OP   PSYCHOLOGT. 

§  46.  Another  class  of  correlations  demands  a  passing 
notice.  Up  to  this  pointy  the  feelings  considered  have  been 
subjective  aspects  of  those  changes  which  objectively  are 
nervous  stimulations.  We  have  now  to  consider  certain 
other  feelings  which  are  the  inner  faces  of  what  on  their 
outer  faces  are  nervous  discharges.  Having  traced  pretty 
fully  the  concomitance  of  sentient  states  and  rccipio-motor 
acts,  it  will  suffice  to  trace  briefly  the  concomitance  of 
sentient  states  and  dirigo-motor  acts. 

Certain  inferior  dirigo-motor  acts  are  unconscious;  but 
omitting  these,  the  law  is  that  with  each  muscular  contraction 
there  goes  a  sensation  more  or  less  definite.  This  is  not  a  sen- 
sation indirectly  produced  through  the  nerves  proceeding  in- 
wards from  the  skin,  some  of  which  are  nearly  always  disturbed 
by  each  bodily  motion ;  but  it  is  a  sensation  directly  pro- 
duced, either  by  the  discharge  itself  or  by  the  state  of  the 
muscle  or  muscles  excited.  It  is  most  clearly  distinguished 
when,  without  touching  anything  and  without  moving,  a 
leg  or  arm  is  held  out  at  right  angles  to  the  body. 

A'^aguo  as  are  feelings  of  this  class  in  comparison  with 
most  feelings  accompanying  nervous  stimulations,  and  much 
less  numerous  as  are  the  varieties  of  quality  among  them, 
they  are  nevertheless  so  far  definite  and  difierent  that  we 
can,  to  a  certain  extent,  recognize  the  separate  feeling  be- 
longing to  each  separate  contraction.  We  are  aware  ■\%'ith- 
out  looking  at  it,  and  without  touching  anything  with  it, 
which  finger  has  been  bent  by  the  discharge  sent  to  its 
flexor  muscles ;  and,  by  the  particular  combination  of  feel- 
ings accompanying  the  act,  the  placing  of  a  limb  in  a  gnven 
attitude  is  present  to  consciousness  without  aid  from  the 
eyes  or  hands.  I  say  we  can  to  a  certain  extent  recognize 
the  changes  we  thus  set  up ;  because  the  differences  among 
the  sensations  of  muscular  tension  soon  lose  much  of  their 
distinctness.  It  is  a  curious  fact  that  when  a  limb  has  been 
held  for  some  time  in  any  position,  especially  if  the  position 
is  one  involving  but  little  strain,  the  subjective  state  asso- 


^STHO-PHYSIOLOGY.  115 

ciatecT  witli  tlie  nervous  discharge  to  its  muscles,  becomes  so 
indefinite  tliat  the  attitude  of  the  limb  is  unknown,  if  there 
does  not  happen  to  be  a  recollection  of  it. 

Besides  the  connection  between  what  we  know  objectively 
as  a  particular  motor  act,  and  subjectively  as  a  particular  feel- 
ing of  muscular  tension,  there  is  a  connection  between  the 
accompanying  motor  excitement  propagated  throughout  the 
muscular  system,  and  a  certain  diffused  feeling  of  which  it 
is  the  seat.  How  along  with  each  special  nervous  discharge 
there  goes  a  general  nervous  discharge,  we  saw  in  the  last 
chapter;  and  here  we  recur  to  the  relation  only  to  observe 
that  there  is  a  parallel  relation  between  the  concomitant 
states  of  consciousness.  Thus  the  vivid  sensation  caused 
by  putting  the  foot  into  scalding  water,  does  not  lead  only 
to  the  muscular  contractions  and  muscular  feelings  which 
accompany  the  sudden  withdrawal  of  the  leg,  but  also  to 
contractions  of  countless  other  muscles  throughout  the 
body,  and  a  feeling  called  a  shock  or  start. 

Nor  are  these  subjective  states,  special  and  general,  that 
accompany  special  and  general  discharges  to  the  muscles, 
the  only  subjective  states  that  accompany  discharges.  As 
before  pointed  out,  the  vascular  system  and  the  alimentary 
system  receive  their  shares  of  each  discharge — very  appre- 
ciable when  it  is  intense,  and  probably  in  no  case  wanting; 
and  these,  too,  present  inner  aspects  to  consciousness.  Some- 
times, indeed,  the  feelings  that  go  along  with  discharges 
into  the  vaso-motor  and  sympathetic  nerves,  are  the  pre- 
dominant ones  ;  as  instance  the  thrill  diffused  thi'ough  the 
body  by  certain  acute  creaking  sounds  said  to  "  set  the 
teeth  on  edge ;"  or  the  nausea  produced  by  particular  kinds 
of  disagreeable  odours. 

§  47.  Are  these  correlations  between  nervous  actions  and 
the  concomitant  feelings  quantitative  ?  Is  there  such  con- 
nection between  a  physical  change  in  the  nervous  system 
and  the  psychical  change  accompanying  it,  that  we  may 


IIG  THE    DATA   OP   PSYCHOLOGY. 

regard  the  one  as  an  equivalent  of  the  other,  in  the  same 
sense  as  ^ye  regard  so  much  heat  as  the  equivalent  of  so 
much  motion  ?  The  reader  will  perhaps  expect  an  affii-ma- 
tive  answer ;  but  if  an  affirmative  answer  is  to  be  given,  it 
must  be  given  in  a  greatly-qualified  form. 

On  remembering  that  many  nervous  actions  are  always 
unconscious ;  on  also  remembering  that  various  objective 
states  of  the  nervous  system  which  have  associated  sub- 
jective states  early  in  life,  cease  to  have  them  later  in  life ; 
and  on  remembering,  further,  that  at  the  same  period  of 
life  a  change  set  up  in  an  afferent  nerve  may  cause  an 
appi'eciable  feeling,  or  may  not  cause  it,  according  as  the 
attention  is  free  or  occupied ;  we  shall  see  that  the  con- 
nection between  feelings  and  nervous  changes  is  con- 
ditioned in  a  very  complex  way,  and  that  if  they 
are  quantitatively  related  it  can  be  only  within  the 
narrow  limits  implied  by  the  complex  conditions.  If  be- 
tween a  purely  voluntary  act  and  a  purely  automatic  act 
there  are  gradations — if,  at  the  one  extreme,  feeling  is  a 
conspicuous  accompaniment,  and,  at  the  other  extreme, 
ceases  to  be  an  accompaniment;  then,  clearly,  in  the  in- 
termediate phases  the  amount  of  feeling  must  bear  a  vary- 
ing ratio  to  the  amount  of  nervous  change  which  the  act 
implies.  Again,    if   we    assume    that   what   is 

present  to  consciousness  as  a  sensation  of  given  strength, 
is  the  correlate  of  a  proportionate  molecular  disturbance  in 
all  the  nervous  structures  concerned,  how  shall  we  interpret 
the  sensations  distinguished  as  subjective  ?  In  sundry  ab- 
normal states,  strono;  feelino's  of  cold  or  heat  are  felt 
throughout  the  body,  though  its  actual  temperature  has 
remained  unaltered.  As  in  any  case  of  this  kind  the  total 
nervous  change  cannot  have  been  the  same  as  if  the  skin 
had  fallen  or  risen  in  temperature  to  the  degree  ordinarily 
required  to  produce  the  feeling,  we  cannot  say  that  there 
is  a  quantitative  equivalence  between  the  amount  of  nervous 
change  and  the  amount  of  feeling.     The  disagreeable  smeU 


a:STHO-PHYSIOL0GT.  117 

whicli,  on  tlie  approach,  of  a  fit,  tliG  epileptic  patient  fre- 
quently complains  of,  affords  a  yet  better  illustration. 
Here  tlie  outer  ends  of  the  afferent  nerves  being  undis- 
turbed, and  only  certain  central  structures  irritated,  the 
quantity  of  nervous  action  is  not  the  same  as  if  the  sensation 
had  been  generated  by  an   actual   smell.  More 

conspicuously  still  do  we  see  the  variability  of  this  rela- 
tion, when  we  compare  the  feelings  called  efforts  with  the 
discharges  and  muscular  strains  produced  by  them  under 
different  conditions.  If  the  psychical  force  known  as  effort 
were  transformable  into  a  constant  quantity  of  physical 
force,  then,  in  any  two  cases,  equal  efforts  should  produce 
equal  contractions.  But  they  do  not.  Great  exertion  in  a 
child  fails  to  evolve  from  its  motor  organs  the  dynamic 
effect  which  a  small  exertion  evolves  from  those  of  a 
man.  Any  one  who  is  fatigued  finds  that  an  intenser 
feeling  of  strain  is  requisite  to  generate  a  given  degree  of 
muscular  tension,  than  when  he  is  fresh.  And  those  pros- 
trated by  illness  show  us  that  immense  expenditures  of  feel- 
ing are  needed  to  perform  acts  which,  during  health,  need 
scarcely  appreciable  expenditures  of  feeling.  Doubtless 
these  differences  are  partly  due  to  differences  in  the 
muscles ;  which,  when  undeveloped  or  when  wasted,  are 
excited  to  smaller  amounts  of  tension  by  equal  amounts  of 
discharge.  But  we  must  regard  them  as  partly  due  to  the 
imperfect  development,  or  the  worn  state,  of  the  interme- 
diate motor  centres  and  efferent  nerves,  in  which  a  given 
feeling  excites  a  smaller  molecular  disturbance  than  when 
they  are  finished  in  structure  and  in  complete  repair — a 
conclusion  enforced  by  the  familiar  experience  that  purely 
nervous  acts,  as  those  of  thought,  require  unusual  efforts 
when  the  brain  is  tried. 

This  variability  of  the  quantitative  relation  between 
nervous  actions  and  psychical  states,  is  equally  seen  when 
we  limit  our  comparisons  to  those  nervous  actions  and 
psychical  states  which  occur  in  the  same  individual  under 


118  THE    DATA   OP    PSYCHOLOGY. 

the  same  bodily  conditions.  To  show  that  unlike  but 
equally  intense  sensations  may  be  produced  by  peripheral 
disturbances  widely  unlike  in  their  amounts,,  providing  they 
arise  in  different  external  sense-organs^  is  scarcely  possible 
without  comparing  the  amounts  of  the  incident  forces; 
and  this  we  cannot  properly  do,  since  we  are  here  confining 
our  attention  to  correlations  within  the  organism.  We  are 
similarly  debarred  from  going  at  length  into  the  quantita- 
tive contrasts  between  the  muscular  tensions  produced  by 
the  same  feeling  of  effort,  according  as  the  muscles  excited 
are  large  or  small ;  for  we  cannot  well  establish  these  con- 
trasts without  measuring  the  inuscular  tensions  by  the 
external  actions  they  are  equivalent  to.  There  is,  however, 
one  class  of  apjjropriate  cases — those  in  which  irritations 
arising  within  the  organism,  set  up  sensations  that  cause 
undirected  motor  discharges.  Violent  toothache,  for  ex- 
ample, is  due  to  waves  of  molecular  change  sent  through 
one  or  two  minute  afferent  nerve-fibres  ;  but  the  bodily 
contortions  show  us  that  the  feeling  so  produced,  sujfices  to 
send  waves  of  molecular  change  through  various  large 
bundles  of  efferent  nerve-fibres,  and  to  contract  numerous 
muscles  Avith  much  force.  To  which  of  these  disturbances, 
centripetal  or  centrifugal,  is  the  feeling  equivalent  ?  We 
cannot  say  to  both,  for  one  is  many  times  the  other  in 
amount ;  and  we  have  no  reason  to  say  that  it  is  equivalent 
to  one  rather  than  to  the  other :  the  rational  inference  being 
that  it  is  not  equivalent  to  either. 

To  understand  the  real  relations  between  objective  and 
subjective  changes  in  the  nervous  sj'Stem,  we  need  but  to 
recall  certain  of  the  conclusions  reached  in  preceding 
chapters.  The  essential  jjrinciple  of  nervous  organiza- 
tion we  have  seen  to  be  that  the  small  amounts  of  mo- 
tion received,  liberate  larger  amounts,  and  these  again 
still  larger  amounts.  A  disturbance  in  the  end  of  an 
afferent  nerve  is  multiplied  as  it  traverses  the  nerve,  and 
the  degree  of  nmltiplication  varies  with  the  length  of  the 


iESTHO-PHYSIOLOGY.  119 

nerve;  it  is  mucL.  more  multiplied  in  fhe  first  ganglion 
readied,  and  increases  further  in  traversing  tlie  centripetal 
nerve ;  it  is  again  multiplied  in  the  superior  centre,  to  be 
afterwards  augmented  in  its  subsequent  centrifugal  course  ; 
and  it  is  once  more  multiplied,  probably  in  a  far  greater 
degree,  in  the  contractile  substance  of  the  excited  muscles. 
Hence  the  accompanying  feeling,  which  is  the  subjective 
aspect  of  this  disturbance  at  one  of  its  intermediate  stages, 
can  be  a  quantitative  equivalent  neither  of  the  initial  nervous 
change  nor  of  the  terminal  nervous  change.  Moreover,  since 
the  multiplication  varies  in  degree,  being  much  greater  in 
the  organs  of  the  higher  senses  than  in  those  of  the  lower, 
it  follows  that  the  ratio  between  the  amount  of  feeling  and 
the  amount  of  initial  change  is  far  from  constant ;  and  the 
evidence  clearly  indicates  a  like  inconstancy  of  the  ratio 
between  the  amount  of  feeling  and  the  amount  of  terminal 
change,  according  as  one  or  other  muscle  or  set  of  muscles 
is  made  to  act. 

How  then  can  there  be  any  quantitative  relation,  it  will 
be  asked.  If  there  is  no  equivalence  between  a  disturbance 
set  up  at  the  periphery  and  the  .produced  feeling,  and  no 
equivalence  between  the  produced  feeling  and  the  motor 
discharge  that  follows — if  the  feeling  does  not  even  bear 
the  same  ratio  to  either  the  initial  or  the  terminal  nervous 
change  in  different  cases ;  what  quantitative  relation  can 
there  be  ?  The  reply  is  simple.  There  is  a  quantitative 
relation  between  nervous  change  and  feeling  when  all  other 
things  remain  the  same ;  and  there  is  a  quantitative  relation 
between  feeling  and  resulting  contraction  when  all  other 
things  remain  the  same.  Supposing  every  condition  to 
continue  unaltered,  then  the  stimulus  conveyed  through 
a  given  nerve  to  a  given  centre,  will  evoke  a  feeling  that 
increases  and  decreases  in  something  like  the  same  pro- 
portion as  the  stimulus  increases  and  decreases;  and,  sup- 
posing a  given  muscle  to  be  contracted,  then  the  amount 
of  its  contraction  will  bear  a  tolerably  constant   ratio  to 


120  THE    DATA    OF  PSYCHOLOGY. 

the  feeling  of  effort  that  accompanies  the  contraction  of 
it.  The  nature  of  these  correlations  may  best  be  expressed 
by  numbers.  If,  coming  through  a  g-iven  afferent  nerve, 
a  disturbance  represented  by  1  generates  a  feeling  repre- 
sented by  5,  then  disturbance  2  will  generate  feeling-  10, 
and  disturbance  5  feeling  25 ;  and  if,  acting  through  a 
given  efferent  nerve,  feeling  5  results  in  muscular  tension 
60,  feeling  10  will  result  in  muscular  tension  120.  But  to 
complete  this  numerical  expression  of  the  facts  we  must 
suppose  these  ratios  to  vary  with  every  set  of  afferent 
nerves  and  every  set  of  efferent  nerves.  If  we  say  that 
1  to  5  represents  the  ratio  of  disturbance  to  feeling-  in  the 
sense  of  touch,  then  to  represent  it  in  the  sense  of  hearing 
will  need,  say,  1  to  100,  and  in  the  sense  of  sight  pei-haps 
'1  to  1,000  ;  and  similarly  with  the  ratios  throughout  the 
motor  apparatus,  according  as  the  muscles  are  large  or 
small. 

In  brief,  then,  the  quantitative  correlation  of  feeling 
and  nervous  change,  holds  true  only  within  narrow  limits. 
We  have  good  reason  to  conclude  that  at  the  particular 
place  in  a  superior  nervous  centre  where,  in  some  mys- 
terious way,  an  objective  change  or  nervous  action  causes  a 
subjective  change  or  feeling,  there  exists  a  quantitative 
equivalence  between  the  two  :  the  amount  of  sensation  is 
proportionate  to  the  amount  of  molecular  transformation 
that  takes  place  in  the  vesicular  substance  affected.  But 
there  is  no  fixed,  or  even  approximate,  quantitative  relation 
between  this  amount  of  molecular  transformation  in  the 
sentient  centre,  and  the  peripheral  disturbance  originally 
causing  it,  or  the  disturbance  of  the  motor  appai'atus  which 
it  may  eventually  cause. 

§  48.  The  feelings  called  sensations  have  alone  been  con- 
sidered thus  far ;  leaving  out  of  view  the  feelings  dis- 
tinguished as  emotions.  Much  less  definite  as  they  are, 
and  not  capable  of  being  made  at  will  the  objects  of  ob- 


.^STHO-PHYSIOLOGY.  121 

servation  and  experiment,  tlie  emotions  are  more  difficult 
to  deal  witli.  But  having  discerned  certain  general  laws 
to  wliicli  the  simpler  feelings  conform,  we  may  now  ask 
whether,  so  far  as  we  can  see,  they  are  conformed  to 
by  the  more  complex  feelings.  We  shall  find  that 
they  are. 

The  conditions  essential  to  the  one  are  essential  to  the 
other.  Emotions,  like  sensations,  may  be  increased  or 
decreased  in  intensity  by  altering  either  the  quantity  or 
the  quality  of  the  blood.  That  general  abundance  of 
blood  is  a  cause  of  emotional  exaltation,  though  tolerably 
certain,  is  not  easily  proved;  but  there  is  sufficient  evidence 
of  the  converse  fact  that,  other  things  equal,  depletion  is  a 
cause  of  apathy.  The  efiect  of  local  abundance  of  blood  is 
undoubted  :  there  is  no  question  that,  within  limits,  the 
amount  of  emotion  varies  as  the  amount  of  blood  supplied 
to  the  great  nervous  centres.  That  nervous  stimulants  in- 
tensify the  emotions,  or,  as  we  say,  raise  the  spirits,  is 
even  more  manifest  than  that  they  make  the  sensations 
keener.  And  it  is  a  familiar  truth  that  sedatives  diminish 
what  is  distinguished  as  moral  pain,  in  the  same  way  that 
they  diminish  pain  arising  in  the  trunk  or  limbs. 

That  a  feeling  lasts  an  appreciable  time,  is  no  less 
true  of  an  emotion  than  of  a  sensation  :  indeed  the  per- 
sistence is  relatively  conspicuous.  The  state  of  conscious- 
ness produced  by  a  flash  of  lightning,  is  so  brief  as  to 
seem  instantaneous  :  only  by  the  help  of  artificial  tests  are 
sensations  of  this  kind  found  to  have  measurable  durations. 
But  no  such  tests  are  needed  to  prove  that  emotions  con- 
tinue through  appreciable  periods.  Even  a  simple  emotion, 
as  of  anger  or  fear,  does  not  reach  its  full  strength  the 
moment  the  cause  presents  itself;  and  after  the  cause  is 
removed  it  takes  some  time  to  die  away.  AVhen  hereafter 
we  deal  with  the  origin  of  emotions,  and  recognize  the 
fact  that  they  are  of  far  more  involved  natures  than  sensa- 
tions,  and  imply  the  co-operation   of  extremely  intricate 


122  THE   DATA   OF   PSYCHOLOGY. 

nervous  structures,  we  sliall  understand  how  tliis  greater 
duration  is  necessitated. 

That  an  emotion,  like  a  sensation,  leaves  behind  it  a  tem- 
porary incapacity,  is  also  true ;  and  as  the  emotion  produced 
by  a  momentary  cause  lasts  longer  than  a  sensation  pro- 
duced by  a  momentary  cause,  so  does  the  partial  incapacity 
for  a  like  emotion  last  longer  than  the  partial  incapacity 
for  a  like  sensation.  Passions  of  all  kinds  come  in  gushes 
or  bursts.  That  they  often  continue  for  hours  and  days, 
is  true ;  but  they  are  never  uniform  throughout  hours 
and  days.  Be  it  in  grief,  or  joy,  or  tenderness,  there  is 
always  a  succession  of  rises  and  falls  of  intensity — a 
paroxysm  of  violent  feeling  with  an  interval  of  feeling  less 
violent,  followed  by  another  paroxysm.  And  then,  after  a 
succession  of  these  comparatively-quick  alternations,  there 
comes  a  calm  —  a  period  during  which  the  waves  of 
emotion  are  feebler :  succeeded,  it  may  be,  by  another 
series  of  stronger  waves.  As  in  the  case  of  the  sensations  so 
in  the  case  of  the  emotions,  this  follows  from  the  fact  that 
what  is  objectively  a  nervous  action  and  subjectively  a 
feeling,  involves  waste  of  the  nervous  structures  concerned. 
The  centres  which  are  the  seats  of  emotions  undergo  dis- 
integration in  the  genesis  of  emotions  ;  and,  other  things 
remaining  equal,  thereupon  become  less  capable  of  genera- 
ting emotions  until  they  are  re-integrated.  I  say,  other 
things  remaining  equal,  because  the  rise  of  an  emotion 
brings  blood  to  the  parts  implicated,  and  so  long  as  the 
afflux  is  increasing  the  intensity  of  the  emotion  may  in- 
ci'case,  notwithstanding  the  waste  that  has  taken  place ; 
but  the  several  conditions  on  which  activity  depends  having 
become  constant,  a  diminished  capacity  for  emotion  inevit- 
ably follows  each  gush  of  emotion. 

That  daily  rises  and  falls  of  strength,  consequent 
on  daily  periodicities  of  waste  and  repair,  occur  in  the 
emotions  as  in  the  sensations,  is  also  tolerably  mani- 
fest.    Cultivated  people,  mostly  leading  lives  that  exercise 


aiSTHO-PHYSIOLOGY.  123 

their  brains  too  much,  and  their  muscles  too  little,  and 
placed  in  social  conditions  that  commonly  bring  the 
strongest  excitements  towards  the  close  of  the  day,  are 
subject  to  an  abnormal  periodicity.  But  those  whose  lives 
conform  best  to  the  laws  of  health,  exhibit  early  in  the 
day  a  general  joyousness  and  emotional  vivacity  greater 
than  they  do  towards  its  close,  when  approaching  sleepi- 
ness is  shown  by  a  flagging  interest  in  the  things  and 
actions  around. 

These  complex  feelings  that  are  centrally  initiated  are 
also  like  the  simple  feelings  that  are  peripherally  initiated, 
in  having  general  discharges  as  well  as  special  discharges : 
indeed  their  general  discharges  are  the  more  conspicuous 
of  the  two.  A  sensation  is  often  visibly  followed  only  by 
local  movement :  unless  veiy  strong  its  effect  on  the  organ- 
ism as  a  whole  is  unobtrusive.  But  an  emotion,  besides 
the  more  obvious  changes  it  works  in  the  muscles  of  the 
face,  habitually  works  changes,  external  and  internal, 
throughout  the  body  at  large.  The  respiration,  the  circula- 
tion, the  digestion,  as  well  as  the  attitudes  and  movements, 
are  influenced  by  it  even  when  moderate ;  and  everyone 
knows  how  strong  passions,  pleasurable  or  painful,  pro- 
foundly disturb  the  whole  system. 

§  49.  Nothing  has  yet  been  said  about  the  most  con- 
spicuous and  most  important  distinction  existing  among 
the  feelings.  Every  feeling,  besides  its  minor  variations  of 
intensity,  exists  under  two  strongly-contrasted  degrees  of 
intensity.  There  is  a  vivid  form  of  it  which  we  call  an 
actual  feeling,  and  there  is  a  faint  form  of  it  which  we  call 
an  ideal  feeling.  What  is  the  nature  of  this  difference  as 
interpreted  from  our  present  stand-point  ? 

When  studying  nerve-structure,  we  saw  that,  in  addition 
to  connections  formed  by  grey  matter  between  the  central 
ends  of  afierent  and  efierent  nerves,  these  have  connec- 
tions   with    centripetal    and    commissural    nirves,    which 


124  THE    DATA   OP    PSYCHOLOGY. 

are  again  connected  witli  more  distant  nerves.  And 
Avlicu  studying  nerve  -  function^  Ave  saw  that  a  disturb- 
ance set  up  by  an  afferent  nerve  in  its  ganglion^  does 
not  affect  exclusively  the  efferent  nerve^  but  that  part 
of  it,  conveyed  through  centripetal  and  commissviral 
nerves,  affects  other  centres,  and  these  again  others,  until 
it  has  reverberated  throughout  the  entire  nervous  system. 
What  follows  ?  These  reverberations  are  feeble  disturb 
ances.  And  every  centre,  liable  as  it  is  to  be  strongl}^ 
disturbed  through  its  afferent  or  centripetal  nerve,  is  liable 
also  to  be  feebly  disturbed  by  these  reverberations  arriving 
through  other  nerves.  What  then  must  hajDpen  with  each 
of  the  libero-motor  elements  composing  those  higher  centres 
in  which  nervous  changes  become  changes  of  consciousness  ? 
AVhen  it  is  affected  through  the  direct  and  fully-opened  route, 
by  that  peripheral  imj^ression  to  which  it  stands  organically 
related,  it  evolves  much  molecular  motion,  becomes  an  active 
propagator  of  disturbances  throughout  the  nervous  system, 
and  is  the  seat  of  what  we  call  a  real  feeling ;  but  when  it 
is  affected  by  these  secondary  waves  diffused  from  other 
strongly  excited  parts,  it  becomes,  as  compared  with  them 
(or  with  itself  under  the  previous  condition)  a  generator  of 
but  little  molecular  motion,  and  is  the  seat  of  that  faint 
feeling  which  we  distinguish  as  ideal.  In  brief,  those 
vivid  states  of  consciousness  which  we  know  as  sensations, 
accompany  direct  and  therefore  strong  excitations  of  nerve- 
centres  ;  while  the  faint  states  of  consciousness  which  we 
know  as  remembered  sensations,  or  ideas  of  sensations, 
accompany  indirect,  and  therefore  weak,  excitations  of 
the  same  nerve-centres. 

That  the  contrast  of  intensity  betweeii  the  effects  of 
direct  and  indirect  excitations,  though  it  holds  generally, 
does  not  hold  without  exception,  is  a  fact  quite  reconcilable 
with  this  interpretation.  For,  on  the  one  hand,  a  direct 
excitation  may  be  very  feeble ;  while,  on  the  other  hand, 
through  a  concurrence  of  diffused  disturbances,  an  indirect 


^STHO-PHYSIOLOGY.  125 

excitation  may  rise  to  considerable  strength.  Hence,  oc- 
casionally, an  ideal  feeling  will  become  almost  or  quite 
equal  in  vividness  to  a  real  feeling.  Especially  may  this 
htippen  when  the  nerve-centre  concerned  is  surcharged  with 
blood ;  since  a  small  disturbance  may  then  set  up  in  it  an 
amount  of  change  equal  to  that  which  a  great  disturbance 
produces  when  only  the  ordinary  quantity  of  blood  is  pre- 
sent. And  it  is  a  matter  of  observation  that  congested 
nerve-centres  are  those  in  which  indirectly-excited  feelings 
reach  an  intensity  scarcely  less  than  that  of  directly-excited 
feelings. 

When  we  pass  from  the  feelings  called  sensations,  of  Avhich 
the  strong  forms  are  peripherally  initiated,  to  the  feelings 
called  emotions,  of  which  the  strong  forms  are  centrally 
initiated,  we  find  the  difference  between  the  strong  and  the 
weak  forms  by  no  means  so  great;  so  that,  in  fact,  ideal 
emotion  passes  into  actual  emotion  without  any  line  of  de- 
marcation. Obviously  this  is  what  might  be  anticipated. 
For  whether  ideal  or  actual,  emotion  is  an  accompaniment 
of  an  indirect  excitation  :  it  is  not  an  immediate  result 
of  peripheral  impressions,  either  simple  or  combined ; 
but  a  mediate  or  remote  result  of  them.  Hence,  all  emo- 
tions, vivid  and  faint,  being  the  subjective  aspects  of  ob- 
jective nervous  changes  that  are  produced  indirectly,  are 
distinguishable  only  according  to  the  degree  of  indirectness 
of  the  excitation,  and  this  admits  of  insensible  gradations. 

§  50.  One  more  general  truth  must  be  set  down  to  com- 
plete the  outline.  The  foregoing  inferences  joined  with 
some  contained  in  the  last  chapter,  introduce  us  to  it. 

In  §§  36,  37,  it  was  pointed  out  that  nerve-centres  dis- 
integrated by  action,  are  perpetually  re-integrating  them- 
selves, and  again  becoming  fit  for  action.  We  saw  that 
repair  partially  makes  up  for  waste  from  instant  to  instant, 
and  that  the  arrears  of  repair  are  made  up  daily  during 
that  period  of  quiescence  when  waste  almost  ceases.     We 


126  THE    DATA   OP    PSYCHOLOGY. 

further  saw  tliat  tlie  restoration  of  a  nerve-centre  to  its  stato 
of  integrity,  is  not  only  the  filling  up  of  its  quantum  of  de- 
composable matter,  but  is  also  the  replacing  of  molecules 
most  exposed  to  disturbance,  and  consequently  the  produc- 
tion of  a  comparatively-unstable  state.  And  we  saw  how, 
after  a  period  of  profound  repose,  there  thus  arises  a  con- 
dition of  the  nerve-centres  such  that  very  slight  stimuli  cause 
nervous  discharges. 

This  law  applies  not  generally  only,  but  specially  to  each 
nerve-centre  and  each  of  its  component  parts.  In  propor- 
tion as  any  part  of  a  nerve-centre  has  been  for  a  long  time 
unused — in  proportion,  that  is,  as  repair  of  it  has  gone  on 
day  after  day  and  night  after  night  unhindered  by  appre- 
ciable waste,  it  must  be  bi-ought  to  a  state  of  more  than 
ordinary  instability — a  state  of  excessive  readiness  to  de- 
compose and  discharge.  What  must  happen  ?  In  common 
with  all  other  parts,  it  is  exposed  to  these  revei-berations 
which  from  instant  to  instant  fill  the  nervous  system.  Its 
extreme  instability  must  render  it  unusually  sensitive  to 
these  reverberations — unusually  ready  to  undergo  change, 
to  yield  up  molecular  motion,  and  to  become  the  seat  of 
the  concomitant  ideal  feeling.  Besides  a  great  liability 
to  the  ideal  feeling  this  same  condition  must  entail  a  great 
sti-eugth  of  it ;  and  so  while  the  instability  continues,  a 
strong  ideal  feeling  will  be  perpetually  aroused.  As, 
however,  the  nerve-centre  in  which  such  secondary  mole- 
cular changes  and  accompanying  ideal  feelings  are  thus  set 
up,  is  somewhat  wasted  by  them,  it  follows  that  after  they 
have  gone  on  for  a  considerable  period  the  instability  of  the 
centre  will  be  diminished :  it  will  no  longer  be  so  easily  de- 
composed by  indirect  disturbances,  and  the  feeling  will  not 
be  produced. 

Here  we  have  the  interpretation  of  what  are  called 
desires.  Desires  are  ideal  feelings  that  arise  when  the 
real  feelings  to  which  they  correspond  have  not  been  ex- 
perienced for  some  time.     They  are  then  liable  to  be  excited 


^STHO-PHYSIOLOOY.  1.27 

by  various  of  tlie  indirect  disturbances  reflected  from  part 
to  part  of  tlie  nervous  system.  They  are  usually  vivid  and 
persistent  in  proportion  to  the  previous  period  of  rest — 
more  vivid  and  more  persistent  than  ideal  feelings  of  the 
same  kind  under  ordinary  conditions.  But  after  a  pro- 
longed period  during  which  they  continue  to  arise  and 
almost  monopolize  consciousness^  they  become  feebler  and 
finally  die  away. 

§  51.  Such  are  the  leading  truths  of  ^stho-Physiology, 
set-  fortli  with  as  much  fulness  as  is  here  requisite.  Sensa- 
tion and  emotion  in  their  relations  to  nervous  action,  have 
been  dealt  with  generally ;  and  whatever  has  been  said  of 
special  sensations  and  special  emotions  has  been  said  merely 
to  illustrate  a  law  which  holds  among  all  the  rest.  The 
concomitants,  subjective  and  objective,  of  each  particular 
kind  of  sensation  and  each  particular  kind  of  emotion, 
I  here  pass  over.  They  may  be  studied  to  great  advantage 
in  the  works  of  Professor  Bain  on  The  Senses  and  the 
Intellect,  and  TIlo  Emotions  and  the  Will;  in  which  he 
has  given  an  elaborate  account  of  the  connection  between 
each  particular  feeling,  simple  or  complex,  and  its  various 
physical  accompaniments.  To  these  works  I  must  com- 
mend the  reader  who  wishes  to  trace  out  these  minor  cor- 
relations. As  data  for  the  present  treatise,  the  only  facts 
needful  to  be  carried  with  us  are  those  set  forth  in  the 
preceding  sections.     They  may  be  summed  up  thus. 

Feeling  of  whatever  kind  is  directly  known  by  each 
person  in  no  other  place  than  his  own  consciousness.  That 
feelings  exist  in  the  world  beyond  consciousness,  is  a  belief 
reached  only  through  an  involved  combination  of  infer- 
ences. That  alike  in  human  and  inferior  beings,  feelings 
are  accompaniments  of  changes  in  the  peculiar  structure 
known  as  the  nervous  system,  is  also  an  indirectly- 
established  belief.  And  that  the  feelings  alone  cognizable 
by  any  individual  are  products   of  the  action  of  his  own 


128  THE    DATA   OP   PSYCHOLOGY. 

nervous  system,  wliicli  he  lias  never  seen  and  on  wliicli  he 
can  try  no  experiments,  is  a  belief  only  to  be  arrived  at 
through  a  further  chain  of  reasoning.  Nevertheless,  the 
evidence,  though  so  indirect,  is  so  extensive,  so  varied,  and 
so  congruous,  that  we  may  accept  the  conclusion  without 
hesitation. 

The  conclusion  having  been  accepted — provisionally  if 
not  permanently — its  validity  is  shown  by  leading  us  to 
anticipate  truly,  in  one  set  of  cases  after  another,  the  par- 
ticular subjective  jjhenomena  that  accompany  particular 
objective  phenomena.  We  have  seen  that  the  several 
circumstances  which  facilitate  or  hinder  nervous  action, 
are  also  circumstances  which  facilitate  or  hinder  feelint?. 
We  have  seen  that  as  nervous  action  occupies  appreciable 
time,  so  feeling  occupies  appreciable  time.  We  have  seen 
that  each  feeling  leaves  a  partial  incapacity  for  a  like  feel- 
ing, as  each  nervous  action  leaves  a  partial  incapacity  for 
a  like  nervous  action.  AVe  have  seen  that,  other  things 
equal,  the  intensities  of  feelings  vary  as  the  intensities  of 
the  correlative  nervous  actions.  We  have  seen  that  the 
difference  between  direct  and  indirect  nervous  disturbances, 
corresponds  to  the  difference  between  the  vivid  feelings 
we  call  real  and  the  faint  feelings  we  call  ideal.  And  we 
have  seen  that  certain  more  special  objective  phenomena 
which  nervous  actions  present,  have  answering  subjective 
phenomena  in  the  forms  of  feeling  we  distinguish  as  desires. 

Thus,  impossible  as  it  is  to  get  immediate  proof  that 
feeling  and  nervous  action  are  the  inner  and  outer  faces  of 
the  same  change,  yet  the  hypothesis  that  they  are  so 
harmonizes  with  all  the  observed  facts;  and,  as  elsewhere 
sliowTi  {First  Princijyles,  §  40)  no  other  verification  is  pos- 
sible for  us  than  that  which  results  from  the  establishment 
of  complete  congruity  among  our  experiences. 


CHAPTEE  YII. 

THE    SCOPE    OF    PSYCHOLOGY. 

§  52.  We  may  now  enter  on  our  special  topic.  Thus  far 
we  have  been  occupied  with  the  data  of  Psychology^  and 
not  with  Psychology  properly  so-called.  Here  leaving  the 
foundations  we  pass  to  the  supersti-ucture. 

Not  a  few  readers  will  be  surprised  by  the  assertion  that 
none  of  the  truths  we  have  been  contemplating  are  psycho- 
logical truths.  Since  the  anatomy  and  physiology  of  the 
nervous  system  have  occupied  so  much  attention^  and  since 
it  has  been  growing  manifest  that  there  is  a  fundamental 
connection  between  nervous  changes  and  psychical  states, 
there  has  arisen  a  confusion  between  the  .phenomena  which 
underlie  Psychology  and  the  phenomena  of  Psychology  itself. 
In  reality,  all  the  facts  ascertained  by  those  who  have  made 
nerve-structure  and  nerve-function  their  studies,  are  facts 
of  a  simpler  order  than  those  rightly  termed  psychological ; 
though  they  are  facts  entering  into  the  composition  of 
psychological  facts. 

Most  will  admit  without  hesitation  that  the  first  five 
chapters  of  this  part  consist  of  propositions  which  are  exclu- 
sively morphological  and  physiological.  In  them  the  struc- 
ture of  the  nervous  system,  its  functions,  the  conditions 
to  its  action,  &c.,  have'  been  dealt  with  purely  as  physical 
phenomena — phenomena  as  purely  physical  as  the  absorption 


130  THE    DATA   OF   PSYCHOLOGY. 

of  nutriment  or  the  circulation  of  tlie  blood.  '\^Tiatever 
implications  may  liave  arisen  from  the  use  of  words  that 
carry  with  them  indirect  meanings,  the  direct  meanings  of 
all  the  propositions  set  down  have  nowhere  implied  con- 
sciousness or  feeling ;  and,  ignoring  consciousness  or  feeling, 
they  have  left  out  that  which  is  tacitly  or  avowedly  contained 
in  every  proposition  of  Psychology. 

It  will  probably  be  thought,  however,  that  at  any  rate 
truths  belonging  to  Psychology  proper  are  to  be  found 
in  the  last  chapter.  Dealing  as  the  last  chapter  does  with 
the  connections  between  nervous  changes  and  feelings,  it 
necessarily  becomes,  by  including  a  psychical  element,  a  part 
of  psychical  science.  To  this  the  rejoinder  is  that,  though 
it  can  scarcely  be  excluded  absolutely  from  the  body  of  this 
science,  yet  it  does  not  strictly  fall  within  that  body,  ^stho- 
physiology  has  a  jDOsition  that  is  entirely  unique.  It  belongs 
neither  to  the  objective  world  nor  the  subjective  world ;  but 
taking  a  term  from  each,  occupies  itself  with  the  correlation 
of  the  two.  It  may  with  as  much  propriety  be  included 
in  the  domain  of  physical  science  as  in  the  domain  of  psy- 
chical science ;  and  must  be  left  where  it  stands,  as  the 
Hnk  between  them. 

Perhaps  this  explanation  will  increase  rather  than  decrease 
the  surprise  produced  by  the  assertion  that  was  to  be  justi- 
fied. To  clear  up  the  confusion,  we  must  examine  more 
carefully  the  distinction  between  the  truths  which  are 
strictly  psychological  and  those  which  merely  enter  into 
the  composition  of  psychological  truths,  y 

§  53.  Throughout  the  preceding  chapters,  including  even 
tlic  last,  every  proposition  set  down  has  expressed  some 
relation  of  phenomena  occurring  within  the  limits  of  the 
orgnnism.  The  subject-matter  has  been  the  character  of 
a  structure ;  or  the  effect  which  a  disturbance  set  up  in  one 
place  has  in  causing  motion  in  another;  or  the  connection 
between   the  physical  state  of  the  whole  or  a  part  of  tho 


THE    SCOPE    OP    rSYC 


organismj  aud  some  general  or  local  nervous  process ;  or 
tlie  variable  intensity  of  an  action  in  a  nerve-centre  as 
determined  by  a  preceding  like  action ;  or  the  interdepen- 
dence of  internal  physical  cbanges  and  internal  psycbical 
changes.  That  is  to  say^  the  attention  has  everywhere  been 
directed  exclusively  to  co-existences  and  sequences  of  which 
the  body  alone  is  the  sphere.  Distinct  or  tacit 

reference  has,  indeed,  frequently  been  made  to  some  external 
force.  Either  a  disturbing  agent  lying  beyond  the  limits  of 
the  organism  has  been  referred  to  in  general  terms,  or,  for 
illustration's  sake,  this  or  the  other  kind  of  disturbing  agent 
has  been  named.  But  such  references,  vague  or  distinct, 
have  been  made  merely  because  it  was  needful  to  suppose 
something  by  which  an  organic  change  was  set  up ;  not 
because  this  something  had  to  be  included  in  the  proposi- 
tion set  down,  which  in  every  case  formulated  an  internal 
x'elation  only.  The  entanglement  of  phenomena  is  such,  that 
we  can  never  cut  off  absolutely  from  all  others  the  par- 
ticular phenomena  we  are  dealing  with;  but,  because  we 
pi'esuppose  these  other  phenomena,  it  does  not  follow  that 
the  science  to  which  they  pertain  forms  part  of  the  science 
■with  which  we  are  specially  occupied.  For  instance,  it  is 
impossible  to  describe,  or  think  of,  a  chemical  experiment 
that  discloses  some  chemical  relation,  without  making  dis- 
tinct or  tacit  references  to  physical  relations — the  pouring 
and  mixture  of  liquids,  the  ascent  of  bubbles  of  disengaged 
gas,  the  falling  of  a  precipitate ;  but  it  is  not  therefore  held 
that  we  are  including  physics  in  our  chemistry.  Similarly, 
it  must  be  admitted  that  though  the  foregoing  chapters 
have  tacitly  assumed  environing  forces,  yet  this  assumption 
has  been  simply  incidental  to  the  study  of  internal  co- 
existences and  sequences. 

Now  so  long  as  we  state  facts  of  which  all  the  terms  lie 
within  the  organism,  our  facts  are  morphological  or  phy- 
siological and  in  no  degree  psychological.  Even  though 
the  relation  with  which  we  are  dealing;  is  that  between  a 


132  THE    DATA   OP    PSYCHOLOGY. 

nervous  ctange  and  a  feeling,  it  is  still  not  a  psycliological 
relation  so  long-  as  tlio  feeling  is  regarded  merely  as  con- 
nected Avitli  tlie  nervous  change,  and  not  as  connected  witli 
some  existence  l3'ing  outside  the  organism.  As  certainly  as 
the  man  who  demonstrates  by  dissection  the  articulations  of 
the  bones,  and  the  man  who,  by  a  sphygmograph,  delineates 
the  varying  motions  of  the  heart,  are  respectively  studying 
morphology  and  physiology;  so  certainly  is  the  man  who 
examines  nervous  structure  and  experiments  on  nervous 
function,  a  student  of  these  same  sciences,  if  he  considers 
the  inner  coi'relations  only  and  does  not  simultaneously 
consider  the  answering  outer  correlations. 

For  that  which  distinguishes  Psychology  from  the  sciences 
on  which  it  rests,  is,  that  each  of  its  propositions  takes  ac- 
count both  of  the  connected  internal  phenomena  and  of  the 
connected  external  phenomena  to  which  they  refer.  In  a  phy- 
siological proposition  an  inner  relation  is  the  essential  sub- 
ject of  thought ;  but  in  a  psychological  proposition  an  outer 
relation  is  joined  with  it  as  a  co-essential  subject  of  thought. 
A  relation  in  the  environment  rises  into  co-ordinate  im- 
portance with  a  relation  in  the  organism.  The  thing  con- 
templated is  now  a  totally  different  thing.  It  is  not  the 
connection  between  the  internal  phenomena,  nor  is  it  the 
connection  between  the  external  phenomena;  but  it  is  ilie 
connection  hetwcen  tJiese  tivo  connections.  A  psychological 
proposition  is  necessarily  compounded  of  two  propositions;, 
of  which  one  concerns  the  subject  and  the  other  concerns 
the  object ;  and  cannot  be  expressed  without  the  four  terms 
which  these  two  propositions  imply.  The  distinction  may 
be  best  explained  by  symbols.  Suppose  that  A  and  B  are 
two  related  manifestations  in  the  environment — say,  the 
colour  and  taste  of  a  fruit ;  then,  so  long  as  we  contemplate 
their  relation  by  itself,  or  as  associated  with  other  external 
phenomena, "  we  are  occupied  with  a  portion  of  physical 
science.  Now  suppose  that  a  and  h  are  the  sensations  pro- 
duced in  the  organism  l)y  this  peculiar  light  which  the  fruit 


THE    SCOPE    OP    PSYCHOLOGY.  133 

reflects,  and  hj  tlie  chemical  action  of  its  juice  on  the 
palate ;  then,  so  long  as  we  study  the  action  of  the  light  on 
the  retina  and  optic  centres,  and  consider  how  the  juice  sets 
up  in  other  centres  a  ner\^ous  change  known  as  sweetness, 
we  are  occupied  with  facts  belonging  to  the  -sciences  of 
Physiology  and  ^stho-physiology.  But  we  pass  into  the 
domain  of  Psychology  the  moment  we  inquire  how  there 
comes  to  exist  within  the  organism  a  relation  between  a  and 
b  that  in  some  way  or  other  corresponds  to  the  relation 
between  A  and  B.  Pyschology  is  exclusively  concerned  with 
this  connection  between  (A  B)  and  (a  h) — has  to  investigate 
its  natm-e,  its  origin,  its  meaning,  &c. 

A  moment^s  introspection  will  now  make  it  clear  to  the 
reader,  that  he  cannot  frame  any  psychological  conception 
without  thus  looking  at  internal  co-existences  and  se- 
quences in  their  adjustments  to  external  co-existences 
and  sequences.  If  he  studies  the  simplest  act  of  per- 
ception, as  that  of  localizing  a  touch  in  some  part  of  his 
skin,  the  indispensable  terms  of  his  inquiry  are : — on  the 
one  hand  a  thing  (1)  and  a  position  (2),  both  of  which 
he  regards  as  objective ;  and  on  the  other  hand  a  sensation 
(3),  and  a  state  of  consciousness  constituting  his  apprehen- 
sion of  position  (4),  both  of  which  he  regards  as  subjective. 
Again,  to  cite  an  example  from  the  opposite  exti-eme, 
if  he  takes  for  his  problem  one  of  his  involved  sentiments, 
as  that  of  justice,  he  cannot  represent  to  himself  this 
sentiment,  or  give  any  meaning  to  its  name,  without  calling 
to  mind  actions  and  relations  supposed  to  exist  in  the 
environment :  neither  this  nor  any  other  emotion  can  be 
aroused  in  consciousness  even  vaguely,  without  positing 
something  beyond  consciousness  to  which  it  refers.  And 
when,  instead  of  studying  Psychology  subjectively,  he 
studies  it  objectively  in  the  acts  of  other  beings,  he 
similarly  finds  himself  incapable  of  stirring  'a  step  with- 
out thinkino;  of  inner  correlations  in  their  references  to 
outer  correlations. 


134  THE    DATA   OP    rSYCHOLOGY. 

/  §  54.  It  is  contended  by  some  that  Psycliology  is  a  part 
of  Biology _,  and  should  be  merged  in  it ;  and  those  who  hold 
this  view  Avill  possibly  answer  the  above  argument  by 
saying  that  in  many  cases  the  non-psychological  pai-t  of 
Biology  also  takes  into  account  phenomena  in  the  enN^ron- 
mcnt^  and  even  definite  connections  among  these  pheno- 
mena. The  life  of  every  organism  is  a  continuous  adaptation 
of  its  inner  actions  to  outer  actions  ;  and  a  complete 
interpretation  of  the  inner  actions  involves  rocog'nition 
of  the  outer  actions.  The  annual  production  of  leaves, 
flowers,  and  seeds  by  plants,  is  adjusted  to  the  annual 
changes  of  the  seasons ;  and  there  is  in  animals  an  adjust- 
ment between  external  changes  in  temperature  and  abund- 
ance, and  internal  production  of  ova.  Moreover,  there  are 
many  special  relations  of  structure  and  function  in  plants 
and  animals,  that  have  reference  to  special  relations  of  struc- 
ture and  function  in  surrounding  plants  and  animals :  in- 
stance those  arrangements  of  the  sexual  organs  that  fit 
particular  phsenogams  for  being  fertilized  l)y  the  particular 
insects  that  visit  them. 

But  true  as  is  this  conception  of  Life  (and  having  based 
the  Principles  of  Biology  on  it  I  am  not  likely  to  question 
or  to  undervalue  it),  I  nevertheless  hold  the  distinction 
above  drawn  to  be  substantially  valid.  For  through- 
out Biology  proper,  the  environment  and  its  correlated 
phenomena  are  either  but  tacitly  recognized,  or,  if  overtly 
and  definitely  recognized,  are  so  but  occasionally ;  while 
the  organism  and  its  correlated  phenomena  practically 
monopolize  the  attention.  But  in  Psyqhology,  the  cor- 
related phenomena  of  the  enwonment  are  at  every  stej) 
avowedly  and  distinctly  recognized ;  and  are  as  essential 
to  every  psychological  idea  as  are  the  correlated  phe- 
nomena of  the  organism.  Let  us  observe  the  contrast 
as  exemplified.  We  study  digestion.  Digestion  implies 
food.  Food  implies  neighbouring  plants  or  animals.  Bat 
this  implication  scarcely  enters  into  our  study  of  digestion. 


THE    SCOPE    OP    PSYCHOLOGY.  135 

unless  we  ask  tlie  quite  special  question — how  the  digestive 
organs  become  fitted  to  the  materials  they  have  to  act  upon  ? 
Again,  when  we  interpret  respiration  we  take  for  granted  a 
surrounding  oxygenated  medium.  And  yet  to  show  how 
far  the  two  may  be  separated,  we  need  only  remember  that 
the  phenomena  of  respiration  may  be  very  well  traced  out 
in  one  who  breathes  a  bladder  of  gas  artificially  obtained 
from  peroxide  of  manganese  or  chlorate  of  potash.  Once 
more,  if,  in  following  out  the  life-history  of  a  plant,  we  have 
to  note  the  adaptation  of  its  hooked  seeds  to  the  woolly 
fleece  of  the  animal  which  accidentally  carries  them  off  and 
disperses  them,  this  distinct  reference  to  specially-connected 
phenomena  in  the  environment,  occurs  either  but  once  in  an 
account  of  the  plant's  life,  or  only  at  long  intervals.  In  fact, 
we  may  say  that  the  great  mass  of  purely  biological  pheno- 
mena may  be  displayed  for  some  time  by  an  organism  de- 
tached from  its  medium,  as  by  a  fish  out  of  water.  Now 
observe  how  different  it  is  with  psychological  phenomena. 
We  cannot  explain  a  single  act  of  a  fish  as  it  moves  about 
in  the  water,  without  taking  into  account  its  relations  to 
neighbouring  objects  distinguished  by  specially-related 
attributes.  The  instinctive  proceedings  of  the  insect, 
equally  with  those  which  in  higher  ci-eatures  we  call  in- 
telligent, we  are  unable  even  to  express  without  referring 
to  things  around. 

In  brief,  then,  the  propositions  of  Biology,  when  they 
imply  the  cnvii'onment  at  all,  imply  almost  exclusively  its 
few  general  and  constant  phenomena,  which,  because  of 
their  generality  and  constancy,  may  be  left  out  of  con- 
sideration; whereas  the  propositions  of  Psychology  refer 
to  its  multitudinous,  special,  and  ever-varying  phenomena, 
which,  because  of  their  speciality  and  changeability,  can- 
not bo  left  out  of  consideration. 

/  §  55.  The  admission  that  Psychology  is  not  demarcated 
from    Biology  by  a  sharp  line,  will  perhaps   be  construed 


136  THE    DATA   OF    PSYCHOLOGY. 

into  the  admission  that  it  cannot  rightly  be  regarded  as  a 
distinct  science.  But  those  who  so  construe  tlie  admission, 
misconceive  the  natures  of  the  relations  among  the  sciences. 
They  assume  that  there  exist  objectively  those  clear  separa- 
tions which  the  needs  of  classification  lead  us  to  make 
subjectively.  Whereas  the  fact  is,  that  beyond  the  divisions 
between  the  three  fundamental  orders  of  the  sciences.  Ab- 
stract, Abstract-concrete,  and  Concrete,  there  exist  ob- 
jectively no  clear  separations  at  all:  there  arc  only  differ- 
ent groups  of  phenomena  broadly  contrasted  but  shading 
off  one  into  another.  To  those  who  accept  the  doctrine  of 
Evolution,  this  scarcely  needs  saying ;  for  Evolution  being 
a  universal  process,  one  and  continuous  throughout/all 
forms  of  existence,  there  can  be  no  break — no  change  from 
one  group  of  concrete  phenomena  to  another  without  a 
bridge  of  intermediate  phenomena.  It  will  be  well  here, 
however,  to  show  by  illustrations  that  the  simpler  concrete 
sciences  are  separable  from  one  another  only  in  the  same 
way  that  Psychology  is  separable  from.  Biology. 

Astronomy  and  Geology  are  regarded  as  distinct.  But 
Geology  is  nothing  more  than  a  chapter  continuing  in 
detail  one  part  of  a  history  that  was  once  wholly  astrono- 
mic ;  and  even  noAv,  many  of  its  leading  facts  belong  as 
much  to  the  older  part  of  the  history  as  to  the  younger. 
Not  only  do  we  trace  back  the  Earth  to  a  time  when  its 
astronomic  attributes  were  uncomplicated  by  those  geo- 
logic ones  that  hare  gradually  arisen  as  it  cooled ;  not  only 
in  the  solar  heat,  causing  the  aerial,  marine,  and  fluvial 
currents  which  work  most  geologic  changes,  are  we  com- 
pelled to  recognize  an  astronomic  force ;  but  in  the  tidal 
wave  we  have  a  phenomenon  as  much  astronomic  as  geo- 
logic, and  as  much  geologic  as  astronomic.  Even  he  who 
arbitrarily  excludes  from  astronomy  everything  but  the 
molar  motions  throughout  the  Solar  System  (so  ignoring 
the  radiant  light  and  heat  by  which  alone  the  Sun  and 
planets  are  known  to  us)   does  not  escape  this  difficulty; 


THE    SCOPE    OP    PSYCHOLOGY.  137 

ft>r  the  motion  of  the  tidal  wave  is  a  molar  motion  gene- 
rated by  forces  such,  as  generate  all  other  molar  motions 
exhibited  by  the  Solar  System ;  and  yet  it  is  at  the  same 
time  a  motion  of  matter  on  the  Earth's  surface,  not  dis- 
tinguishable from  those  other  motions  of  matter  which 
constitute  geological  changes,  many  of  which,  indeed,  are 
concomitants  of  it.  The  separation  between  Bio- 

logy and  Geology  once  seemed  impassable ;  and  to  many 
seems  so  now.  But  every  day  brings  new  reasons  for 
believing  that  the  one  group  of  phenomena  has  grown  out 
of  the  other.  Organisms  are  highly-differentiated  jDortions 
of  the  matter  forming  the  Earth's  crust  and  its  gaseous 
envelope;  and  their  differentiation  from  the  rest  has 
arisen,  like  other  differentiations,  by  degrees.  The  chasm 
between  the  inorganic  and  the  organic  is  being  filled  up. 
On  the  one  hand,  some  four  or  five  thousand  compounds  once 
regarded  as  exclusively  organic,  have  now  been  produced 
artificially  from  inorganic  matter ;  and  chemists  do  not 
doubt  their  ability  so  to  produce  the  highest  forms  of 
organic  matter.  On  the  other  hand,  the  microscope  has 
traced  down  organisms  to  simpler  and  simpler  forms  until, 
in  the  Protogenes  of  Professor  Haeckel,  there  has  been 
reached  a  type  distinguishable  from  a  fragment  of  albumen 
only  by  its  finely-granular  character. 

Thus  the  distinction  between  Biology  and  Psychology  has 
the  same  justification  as  the  distinctions  between  the  con- 
*  Crete  sciences  below  them.  Theoretically,  all  the  concrete 
sciences  are  adjoining  tracts  of  one  science,  Avhich  has  for 
its  subject-matter,  the  continuous  transformation  which  the 
Universe  undergoes.  Practically,  however,  they  are  dis- 
tinguishable as  successively  more  specialized  parts  qf  the 
total  science — parts  further  specialized  by  the  introduction 
of  additional  factors.  The  Astronomy  of  the  Solar  System  is 
a  specialized  part  of  that  general  Astronomy  which  includes 
our  whole  Sidereal  System ;  and  becomes  specialized  by 
taking  into  account  the  revolutions  and  rotations  of  planets 


138  THE    DATA   OF   rSYCIIOLOaY. 

and  satellites.  Geology  (or  rather  Gcogeny  let  ns  call  it, 
that  wc  may  include  all  those  mineralogical  and  m,eteorological 
changes  Avhich  the  word  Geology,  as  now  used,  recognizes 
but  tacitly)  is  a  specialized  part  of  this  special  Astronomy ; 
and  becomes  specialized  by  joining  with  the  effects  of  the 
Earth's  molar  motions,  the  effects  of  continuous  decrease  in 
its  internal  molecular  motion,  and  the  effects  of  the  molecular 
motion  radiated  from  the  Sun.  Biology  is  a  specialized  part 
of  Geogcny,  dealing  with  peculiar  aggregates  of  peculiar 
chemical  compounds  formed  of  the  Earth's  superficial  ele- 
ments— aggregates  which,  while  exposed  to  these  same 
general  forces  molar  and  molecular,  also  exert  certain 
general  actions  and  reactions  on  one  another.  And  Psy- 
chology is  a  specialized  part  of  Biology,  limited  in  its  appli- 
cation to  the  higher  division  of  these  peculiar  aggregates, 
and  occupying  itself  exclusively  with  those  special  actions 
and  reactions  which  they  display,  from  instant  to  instant, 
in  their  converse  with  the  special  objects,  animate  and  in- 
animate, amid  which  they  move. 

But  this  introduction  of  additional  factors,  which  differ- 
entiates each  more  special  science  from  the  more  general 
science  including  it,  fails  in  every  case  to  differentiate  it 
absolutely ;  because  the  introduction  of  the  additional 
factors  is  gradual.  It  is  so  not  with  the  Concrete  Sciences 
alone,  but  even  with  the  Abstract-concrete  Sciences,  which 
at  first  sight  seem  sharply  demarcated ;  as,  for  instance, 
Physics  and  Chemistry.  Physics,  dealing  with  changes  in 
the  distribution  of  matter  and  motion  considered  apart 
from  unlikenesses  of  quality  in  the  matter,  is  obliged  to 
include  in  its  inquiries  all  the  molecular  integrations  and 
disintegrations  caused  by  alterations  of  temperature — the 
meltings  and  evaporations  which  increase  of  heat  produces, 
as  well  as  the  condensations  and  crystallizations  which  follow 
decrease  of  heat.  Among  other  molecular  ti-ansformations 
resulting  from  losses  and  gains  of  molecular  motion,  are 
those  known  as  allotropic — transformations  which,  without 


THE    SCOPE    OP    PSYCHOLOGY.  139 

appreciably  altering  the  degrees  of  integration,  leave  the 
molecules  so  re-arranged  that  they  exhibit  new  properties  of 
the  order  we  call  chemical:  as  is  shown  bv  their  chansred 
affinities  for  the  molecules  of  other  substances,  and  by  their 
changed  effects  on  our  nerves  of  sense.  Must  we  class  such 
molecular  transformations  as  physical  phenomena,  because 
in  each  case  the  molecules  concerned  are  all  of  one  kind  ? 
If  so,  what  are  we  to  say  of  isomeric  transformations,  which 
all  chemists  recognize  as  of  essentially  the  same  nature  ? 
In  these,  molecules  of  different  kinds  are  concerned.  And 
if,  because  they  show  us  a  re-distribution  of  heterogeneous 
molecules  instead  of  homogeneous  ones,  we  put  them  in  the 
category  of  chemical  phenomena,  we  arbitrarily  dissociate 
two  fundamentally-similar  classes  of  facts.  Perhaps  it  will 
be  replied  that  in  isomeric  transformations  the  molecules  are 
homogeneous,  relatively  to  the  re-distribution  they  undergo ; 
that  each  of  them,  retaining  its  individuality  unchanged, 
comports  itself  towards  the  rest  as  though  it  were  a  simple 
molecule ;  that  nothing  more  takes  place  than  a  re -grouping 
of  these  unchanged  molecules ;  and  that  there  is  thus  an 
absence  of  what  constitutes  a  truly  chemical  change — union 
or  disunion  of  unlike  molecules.  The  reply  is  plausible,  but 
it  is  easily  disposed  of.  For  there  are  transformations  of 
this  nature  in  which  such  unions  and  disunions  occur.  A 
colloid  compound  in  passing  from  one  of  its  isomeric  forms 
to  another,  very  generally  parts  with  some  of  its  contained 
water,  or  takes  up  additional  water.  Does  this  make  the 
change  a  chemical  one  ?  Then  we-  must  relegate  to  the 
domain  of  Physics  that  isomei*isni  which  is  not  accompanied 
by  loss  or  gain  of  water,  and  include  in  the  domain  of  Che- 
mistry that  isomerism  which  is  so  accompanied — a  very 
artificial  disunion  of  the  sciences,  to  which  I  think  neither 
Physicists  nor  Chemists  will  agree.  Nevertheless,  un- 
decided as  is  the  line  which  separates  them,  we  are  not 
prevented  from  recognizing  the  broad  distinction  between 
Itlolecular  Physics  and  Chemistry.     The  new  factor  which 


140  THE    DATA   OP   PSYCHOLOGY. 

differentiates  Chemistry  from  Molecular  Physics,  is  the 
heterogeneity  of  the  molecules  with  Avhose  re-distributions 
it  deals.  And  the  contrast  hence  resulting  is  too  strongly 
marked  to  be  obliterated  by  transitional  cases. 

In  this  way  it  is,  then,  that  the  conspicuous  presence 
of  additional  factors  differentiates  Psychology  from  Biology 
proper ;  although  in  Biology  proper  these  factors  make  an 
occasional  appearance.  The  contrast  between  the  two  is  no 
more  destroyed  by  such  community  as  exists,  than  is  the 
contrast  between  night  and  day  destroyed  by  the  occurrence 
of  a  dawn  which  belongs  as  much  to  one  as  to  the  other. 

§  56.  A  far  more  radical  distinction  remains  to  be  drawn. 
While,  under  its  objective  aspect.  Psychology  is  to  be  classed 
as  one  of  the  concrete  sciences  which  successively  decrease 
in  scope  as  they  increase  in  speciality;  under  its  subjective 
aspect,  Psychology  is  a  totally  unique  science,  independent 
of,  and  antithetically  opposed  to,  all  other  sciences  whatever. 
The  thoughts  and  feehngs  which  constitute  a  consciousness, 
and  are  absolutely  inaccessible  to  any  but  the  possessor  of 
that  consciousness,  form  an  existence  that  has  no  place 
among  the  existences  with  which  the  rest  of  the  sciences 
deal.  Though  accumulated  observations  and  experiments 
have  led  us  by  a  very  indirect  series  of  inferences  (§  41)  to  the 
"belief  that  mind  and  nervous  action  are  the  subjective  and 
objective  faces  of  the  same  thing,  we  remain  utterly  incapable 
of  seeing,  and  even  of  imagining,  how  the  two  are  related. 
Mind  still  continues  to  us  a  something  without  any  kinship 
to  other  things;  and  from  the  science  which  discovers  by  in- 
trospection the  laws  of  this  something,  there  is  no  passage 
by  transitional  steps  to  the  sciences  which  discover  the  laws 
of  these  other  things. 

Following  M.  Comte,  there  are  a  few  who  assert  that  a 
subjective  Psychology  is  impossible  ;  and  to  such  the  above 
paragraph  will,  I  suppose,  be  meaningless.  But  whoever 
recognizes  a  subjective  Psychology,  and  admits,  as  he  must. 


THE    SCOPE   OF    PSYCHOLOGY.  141 

that  vritliout  it  there  can  be  no  objective  Psychology,  there- 
upon finds  himself  obliged  to  assign  a  quite  special  rank, 
not  to  the  first  only,  but,  by  implication,  to  the  second.  To 
those  who  see  that  the  essential  conceptions  on  which  Psy- 
chology in  general  proceeds,  ai'e  fui'nished  by  subjective 
Psychology — to  those  who  see  that  such  words  as  feelings, 
ideas,  memories,  volitions,  have  acquired  their  several  mean- 
ings through  self-analysis,  and  that  the  distinctions  we 
make  between  sensations  and  emotions,  or  between  auto- 
matic acts  and  voluntary  acts,  can  be  estabhshed  only  by 
comparisons  among,  and  classifications  of,  our  mental  states; 
it  ^^411  be  manifest  that  objective  Psychology  can  have  no 
existence  as  such,  without  borrowing  its  data  from  sub- 
jective Psychology.  And  thus  perceiving  that,  until  it 
acknowledges  its  indebtedness  to  subjective  Psychology, 
objective  Psychology  cannot  legitimately  use  any  terms  that 
imply  consciousness,  but  must  limit  itself  to  nervous  co- 
ordinations considered  as  physical  only;  they  will  see  that 
even  objective  Psychology  contains  an  element  which  differ- 
entiates it  from  the  rest  of  the  special  concrete  sciences 
more  than  any  of  these  are  differentiated  from  one  another. 
The  claims  of  Psychology  to  rank  as  a  distinct  science, 
are  thus  not  smaller  but  greater  than  those  of  any  other 
science.  If  its  phenomena  are  contemplated  objectively, 
■merely  as  nervo-muscular  adjustments  by  which  the  higher 
organisms  from  moment  to  moment  adapt  their  actions  to 
environing  co-existences  and  seqviences,  its  degree  of 
speciality,  even  then,  entitles  it  to  a  separate  place.  The 
moment  the  element  of  feeling,  or  consciousness,  is  used 
to  interpi-et  nervo-muscular  adjustments  as  thus  exhibited 
in  the  living  beings  around,  objective  Psychology  acquires 
an  additional,  and  quite  exceptional,  distinction.  And  it  is 
further  distinguished  in  being  linked  by  this  common 
element  of  consciousness,  to  the  totally-independent  science 
of  subjective  Psychology — the  two  forming  together  a 
double  science  which,  as  a  whole,  is  quite  sui  generis. 


142  THE    DATA   OF    rSYCIIOLOGY. 

§  57.  So  understanding  its  scope^  wc  are  now  prepared  to 
enter  on  tlie  study  of  Psycliology  proper.  The  foregoing 
discussion  serves  not  unfitly  to  introduce  tlie  several  divi- 
sions into  wliicli  tlie  entire  subject  falls. 

First  come  tlie  Inductions  of  Psycliology;  under  which 
title  wo  will  deal  Avith  the  leading  empirical  generaliza- 
tions— presenting  them,  however,  under  an  aspect  some- 
what different  from  the  usual  one.  And  the  truths  in- 
ductively reached  will,  when  possible,  be  elucidated  deduc- 
tively, by  affiliating  them  on  the  truths  of  Neuro-jDhysiology 
and  ^stho-physiology  set  down  in  the  foregoing  chapters. 

We  will  next  pass  to  Objective  Psychology;  of  which  three 
divisions  may  conveniently  be  made.  In  the  first,  or 
General  Synthesis,  we  will  trace  throughout  the  animal 
kingdom,  the  progress  in  these  perpetual  adjustments  of 
special  inner  actions  to  special  outer  actions,  which  accom- 
panies increasing  evolution  of  the  nervous  system — omitting, 
so  far  as  may  be,  the  element  of  consciousness.  In  the 
second,  or  Special  Synthesis,  we  "will  consider  this  same 
progress  more  closely,  with  the  view  of  delineating  and 
formulating  it  in  terms  that  imply  consciousness.  And  in 
the  third,  or  Physical  Synthesis,  an  endeavour  will  be  made 
to  show  how,  by  an  ultimate  principle  of  nervous  action, 
this  progress  is  explicable  as  part  of  Evolution  in  general. 

Turning  then  to  Subjective  Psychology,  the  natures  of 
particular  modes  of  consciousness,  as  ascertained  by  in- 
trospection, will  first  be  treated  under  the  head  of  Special 
Analysis.  And  then,  under  the  head  of  General  Analysis, 
we  will  enter  upon  the  ultimate  question  of  the  relation 
between  Thought  and  Things. 

Two  remaining  divisions  will  be  devoted,  the  one  to  a 
comparison  between  the  results  reached  in  the  preceding- 
divisions,  with  a  view  of  shoAving  their  congruity,  and  the 
other  to  a  series  of  corollaries  constituting  that  s^^ecial  part 
of  Human  Psychology  on  which  Sociology  must  be  based. 


V    T 

14  DAY  USE 

RETURN  TO  DESK  FROM  WHICH  BORROWED 

ffiUCMlON-PSYCHOLOGY 

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